Aerogel composite powder

ABSTRACT

The present invention relates to an aerogel composite powder superior in thermal insulation and flexibility, the aerogel composite powder comprising an aerogel component and a silica particle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application filed under 35U.S.C. § 371 of International Application No. PCT/JP2017/012610, filedMar. 28, 2017, designating the United States, which claims priority fromJapanese Patent Application No. 2016-065279, filed Mar. 29, 2016, whichare hereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to an aerogel composite powder.

BACKGROUND ART

Silica aerogels are known as materials having thermal insulation withlow thermal conductivity. Silica aerogels are useful as functional rawmaterials with superior functionality (e.g., thermal insulation), uniqueoptical properties, unique electric properties, etc., and used for, forexample, materials for electronic substrates, which utilize the propertyof an ultralow dielectric constant of a silica aerogel, thermalinsulation materials, which utilize the high thermal insulation of asilica aerogel, and light reflective materials, which utilize theultralow refractive index of a silica aerogel.

Supercritical drying is known as a method for producing such a silicaaerogel, in which a gel compound (alcogel) obtained by hydrolyzing andpolymerizing an alkoxysilane is dried under supercritical conditions fora dispersion medium (e.g., see Patent Literature 1). Supercriticaldrying is a method in which an alcogel and a dispersion medium (asolvent used for drying) are introduced into a high-pressure container,and a temperature and pressure equal to or higher than the criticalpoint of the dispersion medium is applied to the dispersion medium toconvert it into a supercritical fluid, thereby removing the solventcontained in the alcogel. However, supercritical drying requires ahigh-pressure process, and hence needs capital investment for specialapparatuses or the like capable of enduring supercritical condition, aswell as much time and effort.

In view of this, techniques of drying an alcogel with a versatile methodwithout need of any high-pressure process have been proposed. A knownexample of such a method is a method in which monoalkyltrialkoxysilaneand tetraalkoxysilane are used in combination with a specific ratio asgel materials to enhance the strength of the resulting alcogel, and thealcogel is dried under ambient pressure (e.g., see Patent Literature 2).When such ambient pressure drying is employed, however, the gel tends toshrink because of a stress caused by capillary force in the inside ofthe alcogel.

CITATION LIST Patent Literature

Patent Literature 1: U.S. Pat. No. 4,402,927

Patent Literature 2: Japanese Unexamined Patent Publication No.2011-93744

SUMMARY OF INVENTION Technical Problem

Although attempts have been made from various viewpoints to overcomeproblems inherent in conventional production processes as describedabove, aerogels produced with any of the processes have low mechanicalstrength, and hence have disadvantages such as brittleness. For example,an aerogel obtained with any of the processes may be broken only onundergoing stress such as compression. The reason is probably that thedensity of the aerogel is low and that the aerogel has a porousstructure in which fine particles with a size of around 10 nm are onlyweakly linked together. An aerogel powder obtained by powdering such abrittle aerogel also has low mechanical strength, and the pore structureof the powder may be broken by stress applied in a process of mixing orkneading with resin.

The present disclosure was made in consideration of the above-describedcircumstances, and an object of the present disclosure is to provide anaerogel composite powder superior in thermal insulation and flexibility.

Solution to Problem

The present inventors diligently studied to achieve the object, andfound that superior thermal insulation and superior flexibility areexhibited when a composite of a silica particle is formed in an aerogel.

The present disclosure provides an aerogel composite powder comprisingan aerogel component and a silica particle. In contrast to aerogelpowders obtained by using any of conventional techniques, the aerogelcomposite powder according to the present disclosure is superior inthermal insulation and flexibility.

The aerogel composite powder can have: a three-dimensional networkskeleton formed of the aerogel component and the silica particle; and apore. Thereby, it becomes easier to further improve thermal insulationand flexibility.

The present disclosure provides an aerogel composite powder comprising asilica particle as a component constituting a three-dimensional networkskeleton. The aerogel composite powder obtained in this manner issuperior in thermal insulation and flexibility.

The present disclosure provides an aerogel composite powder as a driedproduct of a wet gel, wherein the wet gel is a condensate of a solcomprising: a silica particle; and at least one selected from the groupconsisting of a silicon compound having a hydrolyzable functional groupor a condensable functional group and a hydrolysis product of thesilicon compound having a hydrolyzable functional group. The aerogelcomposite obtained in this manner is superior in thermal insulation andflexibility.

The above-described aerogel composite powders may be each a driedproduct of a wet gel, wherein the wet gel is a condensate of a solcomprising: a silica particle; and at least one selected from the groupconsisting of a silicon compound having a hydrolyzable functional groupor a condensable functional group and a hydrolysis product of thesilicon compound having a hydrolyzable functional group.

In the present disclosure, the silicon compound can further comprise apolysiloxane compound having a hydrolysable functional group or acondensable functional group. Thereby, more superior thermal insulationand more superior flexibility can be achieved.

The polysiloxane compound can include a compound having a structurerepresented by the following formula (B):

wherein R^(1b) represents an alkyl group, an alkoxy group, or an arylgroup; R^(2b) and R^(3b) each independently represent an alkoxy group;R^(4b) and R^(5b) each independently represent an alkyl group or an arylgroup; and m represents an integer of 1 to 50.

The aerogel composite can be in a mode having a ladder-type structureincluding struts and a bridge, wherein the bridge has a structurerepresented by the following formula (2):

wherein R⁵ and R⁶ each independently represent an alkyl group or an arylgroup; and b represents an integer of 1 to 50.

The aerogel composite can have a ladder-type structure represented bythe following formula (3):

wherein R⁵, R⁶, R⁷, and R⁸ each independently represent an alkyl groupor an aryl group; a and c each independently represent an integer of 1to 3000; and b represents an integer of 1 to 50.

The average primary particle diameter of the silica particle can be 1 to500 nm. Thereby, it becomes easier to further improve thermal insulationand flexibility.

In this case, the shape of the silica particle can be spherical. Thesilica particle can be an amorphous silica particle, and the amorphoussilica particle can be at least one selected from the group consistingof a fused silica particle, a fumed silica particle, and a colloidalsilica particle. Thereby, more superior thermal insulation and moresuperior flexibility can be achieved.

In the present disclosure, the average particle diameter D50 of theaerogel composite powder can be 1 to 1000 μm. Thereby, gooddispersibility and good handleability can be achieved.

Advantageous Effects of Invention

The present disclosure can provide an aerogel composite powder superiorin thermal insulation and flexibility. Specifically, the presentdisclosure can provide an aerogel composite powder which exhibitssuperior thermal insulation and is flexible and less likely to be brokeneven on undergoing stress such as compression. The aerogel compositepowder, which is superior in thermal insulation and flexibility asdescribed above, has potential utility for a wide variety ofapplications. Here, an important point of the present disclosure is thatthe thermal insulation and flexibility can be controlled more easilythan those of conventional aerogel powders. This is a matter whichconventional aerogel powders have not achieved, because conventionalaerogel powders need to sacrifice the thermal insulation for flexibilityor to sacrifice the flexibility for thermal insulation. The phrase“superior in thermal insulation and flexibility” does not necessarilymean that numerical values as indicators of the two properties are bothlarge, and encompasses, for example, “superior in flexibility with thethermal insulation satisfactorily maintained” and “superior in thermalinsulation with the flexibility satisfactorily maintained”.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a diagram schematically illustrating the microstructure ofan aerogel composite according to an embodiment of the presentinvention.

FIG. 2 shows a diagram for description of a method for calculating thebiaxial average primary particle diameter of a particle.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail occasionally with reference to the drawings.However, the present disclosure is not limited to the embodiments below.In the present specification, a numerical range expressed with “to”represents a range including the numerical values set forth before andafter “to” as the minimum value and the maximum value, respectively.When the phrase “A or B” is used, it is only required to include one ofA and B, and both of A and B may be included. With respect to materialsexemplified in the present embodiments, one material may be used singly,or two or more materials may be used in combination, unless otherwisestated.

<Aerogel Composite Powder>

In a narrow sense, dry gel obtained by using supercritical drying forwet gel is referred to as aerogel, dry gel obtained by drying under theatmospheric pressure is referred to as xerogel, and dry gel obtained byusing freeze drying is referred to as cryogel; however, a dry gel withlow density obtained by using any of these techniques for drying wet gelis referred to as “aerogel” in the present embodiments. That is, theterm “aerogel” in the present embodiments means aerogel in a broadsense, namely, “Gel comprised of a microporous solid in which thedispersed phase is a gas”. In general, the inside of aerogel is formedof a fine network structure, and has a cluster structure in whichaerogel particles (particles constituting the aerogel) with a size ofaround 2 to 20 nm are bonded together. Among skeletons formed in thecluster, pores with a size smaller than 100 nm are present. For thisreason, aerogel has a three-dimensional fine porous structure. Aerogelin the present embodiments is, for example, silica aerogel, whichcomprises silica as a primary component. Examples of the silica aerogelinclude silica aerogel with an organic group (e.g., a methyl group) oran organic chain introduced therein, what is calledorganic-inorganic-hybridized silica aerogel. The aerogel compositepowder (also expressed as the powdery aerogel composite) in the presentembodiments includes a composite of a silica particle in an aerogel, andat the same time has a cluster structure, which is a feature of theaerogel, and thus is a powder having a three-dimensional fine porousstructure.

The aerogel composite powder in the present embodiments comprises anaerogel component and a silica particle. In another possible expression,although the expression does not necessarily have the same meaning asthe previously-mentioned concept, the aerogel composite powder in thepresent embodiments comprises a silica particle as a componentconstituting a three-dimensional network skeleton. The aerogel compositepowder in the present embodiments is superior in thermal insulation andflexibility as described later. In particular, the superior flexibilityresults in provision of an aerogel composite powder which is flexibleand less likely to be broken even on undergoing stress such ascompression. Such an aerogel composite powder is obtained by allowing asilica particle to be present in the environment of aerogel production.The advantage by allowing a silica particle to be present is not onlythat the thermal insulation, flexibility, and so on of the aerogelcomposite powder itself can be improved, but also that reduction of timefor a step of forming wet gel, which is described later, andsimplification of steps from a step of washing and solvent displacementto a step of drying can be achieved. It should be noted that thereduction of time for the step and the simplification of the steps arenot necessarily required in production of an aerogel composite powdersuperior in flexibility.

In the present embodiments, various modes for the composite of theaerogel component and the silica particle are contemplated. For example,the aerogel component may be in an irregular shape such as a film, or beparticulate (aerogel particle). In any mode, the aerogel component invarious forms is present in between the silica particles, which isinferred to impart flexibility to the skeleton of the composite.

Examples of modes for the composite of the aerogel component and thesilica particle include a mode in which the aerogel component in anirregular shape exists between the silica particles. Specific examplesof such a mode include various modes including: a mode in which thesilica particle is covered by a film of the aerogel component (siliconecomponent) (a mode in which the aerogel component includes the silicaparticle therein); a mode in which the silica particles are bonded witheach other via the aerogel component as a binder; a mode in which theaerogel component fills a plurality of voids of the silica particle; anda mode of combination of these modes (e.g., a mode in which a clusterarray of the silica particle is covered by the aerogel component). Asjust described, the three-dimensional network skeleton of the aerogelcomposite powder in the present embodiments can be constituted with thesilica particle and the aerogel component (silicone component), and thespecific mode (embodiment) thereof is not limited in any way.

On the other hand, the aerogel component in the present embodiments mayform a definite particulate composite, not in an irregular shape, withthe silica particle as illustrated in FIG. 1 as described later.

Although the mechanism of formation of such various modes in the aerogelcomposite powder in the present embodiments is not necessarily clear,the present inventor suspects the formation rate of the aerogelcomponent in a step of gelling to be involved therein. For example, theformation rate of the aerogel component tends to vary as the number ofsilanol groups of the silica particle varies. In addition, the formationrate of the aerogel component tends to vary as the pH of the systemvaries.

These suggest that the mode of the aerogel composite powder (e.g., thesize and the shape of the three-dimensional network skeleton) can becontrolled through adjustment of the size, shape, and number of silanolgroups of the silica particle, and the pH and so on of the system.Accordingly, the density, porosity, and so on of the aerogel compositecan be controlled, and hence the thermal insulation and flexibility ofthe aerogel composite can be controlled. The three-dimensional networkskeleton of the aerogel composite powder may be constituted with onlyone of the above-described various modes, or with two or more of themodes.

Now, the aerogel composite powder in the present embodiments will bedescribed with reference to FIG. 1 as an example, though the presentdisclosure is not limited to the mode in FIG. 1 as described above.However, the following description can be appropriately referred to withregard to matters common among the above modes (e.g., the type, size,content of the silica particle).

FIG. 1 shows a diagram schematically illustrating the microstructure ofan aerogel composite powder according to an embodiment of the presentdisclosure. As illustrated in FIG. 1, an aerogel composite 10 has: athree-dimensional network skeleton formed of three-dimensional randomlinkage of an aerogel particle 1 constituting the aerogel component witha silica particle 2 partially intervening; and a pore 3 surrounded bythe skeleton. In this case, the silica particles 2 are present inbetween the aerogel particles 1, and inferred to function as a skeletonsupport to support the three-dimensional network skeleton. Hence, thisstructure probably imparts moderate strength to aerogel while thermalinsulation and flexibility as aerogel are maintained. It follows thatthe aerogel composite powder in the present embodiments may have athree-dimensional network skeleton formed of three-dimensional randomlinkage of a silica particle with an aerogel particle intervening. Thesilica particle may be covered by the aerogel particle. The aerogelparticle (aerogel component) is constituted with a silicon compound, andhence inferred to have high affinity to the silica particle. Probablyfor this reason, the silica particle was successfully introduced intothe three-dimensional network skeleton of aerogel in the presentembodiments. In this regard, silanol groups of the silica particleprobably contribute to the affinity between the aerogel particle and thesilica particle.

The aerogel particle 1 is inferred to be in a mode of a secondaryparticle constituted with a plurality of primary particles, andgenerally spherical. The average particle diameter (i.e., secondaryparticle diameter) of the aerogel particle 1 can be 2 nm or larger, andmay be 5 nm or larger or 10 nm or larger. The average particle diametercan be 50 μm or smaller, and may be 2 μm or smaller or 200 nm orsmaller. In other words, the average particle diameter can be 2 nm to 50μm, and may be 5 nm to 2 μm or 10 nm to 200 nm. It becomes easier toobtain an aerogel composite powder superior in flexibility by settingthe average particle diameter of the aerogel particle 1 to 2 nm orlarger, and, on the other hand, it becomes easier to obtain an aerogelcomposite powder superior in thermal insulation by setting the averageparticle diameter to 50 μm or smaller. The average particle diameter ofthe primary particle constituting the aerogel particle 1 can be 0.1 nmto 5 μm because of easiness in forming a secondary particle with aporous structure of low density, and may be 0.5 nm to 200 nm or 1 nm to20 nm.

Any silica particle can be used for the silica particle 2 without anylimitation, and examples thereof include an amorphous silica particle.Examples of the amorphous silica particle include at least one selectedfrom the group consisting of a fused silica particle, a fumed silicaparticle, and a colloidal silica particle. Among them, the colloidalsilica particle has high monodispersity and facilitates prevention ofaggregation in a sol. The silica particle 2 may be a silica particlehaving a hollow structure, a porous structure, or the like.

The shape of the silica particle 2 is not limited in any way, andexamples thereof include a sphere, a cocoon, and an association. Use ofthe spherical particle among them as the silica particle 2 facilitatesprevention of aggregation in a sol. The average primary particlediameter of the silica particle 2 can be 1 nm or larger, and may be 5 nmor larger or 20 nm or larger. The average primary particle diameter canbe 500 nm or smaller, and may be 300 nm or smaller or 100 nm or smaller.In other words, the average primary particle diameter can be 1 to 500nm, and may be 5 to 300 nm or 20 to 100 nm. By setting the averageprimary particle diameter of the silica particle 2 to 1 nm or larger, itbecomes easier to impart moderate strength to aerogel and obtain anaerogel composite powder superior in shrinkage resistance in drying. Bysetting the average primary particle diameter to 500 nm or smaller, onthe other hand, it becomes easier to suppress the solid thermalconduction of the silica particle and obtain an aerogel composite powdersuperior in thermal insulation.

The aerogel particle 1 (aerogel component) and the silica particle 2 areinferred to be bonding together in a mode of hydrogen bonding orchemical bonding. In this situation, the hydrogen bonding or chemicalbonding is probably formed of a silanol group or reactive group of theaerogel particle 1 (aerogel component) and a silanol group of the silicaparticle 2. Therefore, it probably becomes easier to impart moderatestrength to aerogel if the mode of bonding is chemical bonding. In viewof this, the particle to form a composite with the aerogel component isnot limited to the silica particle, and an inorganic particle or organicparticle having a silanol group on the particle surface can be alsoused.

The number of silanol groups of the silica particle 2 per 1 g can be10×10¹⁸ to 1000×10¹⁸ groups/g, and may be 50×10¹⁸ to 800×10¹⁸ groups/gor 100×10¹⁸ to 700×10¹⁸ groups/g. By setting the number of silanolgroups of the silica particle 2 per 1 g to 10×10¹⁸ groups/g or more, thesilica particle 2 can have better reactivity with the aerogel particle 1(aerogel component), and it becomes easier to obtain an aerogelcomposite powder superior in shrinkage resistance. By setting the numberof silanol groups of the silica particle 2 per 1 g to 1000×10¹⁸ groups/gor less, it becomes easier to prevent rapid gelling in production of asol and obtain a homogeneous aerogel composite powder.

In the present embodiments, the average particle diameter of a particle(e.g., the average secondary particle diameter of the aerogel particle,the average primary particle diameter of the silica particle) can bedetermined through direct observation of a cross-section of the aerogelcomposite by using a scanning electron microscope (hereinafter,abbreviated as “SEM”). For example, individual particle diameters can bedetermined for the aerogel particle or the silica particle on the basisof the diameter of the cross-section of the three-dimensional networkskeleton. The diameter here refers to a diameter when the cross-sectionof a skeleton forming the three-dimensional network skeleton is regardedas a circle. The diameter when the cross-section is regarded as a circlerefers to a diameter of a circle with an area equal to that of thecross-section. In calculation of an average particle diameter, thediameter of a circle is determined for 100 particles, and the diametersare averaged.

The average particle diameter of the silica particle can be determinedfrom measurement for the raw material. For example, the biaxial averageprimary particle diameter can be calculated from results of observationof arbitrarily selected 20 particles by using SEM as follows. Taking acolloidal silica particle with a solid concentration of 5 to 40% bymass, which is typically dispersed in water, as an example, a 2 cm×2 cmchip cut out of a wafer with a wiring pattern is soaked in a dispersionof the colloidal silica particle for approximately 30 seconds, and thechip is then rinsed with pure water for approximately 30 seconds anddried with nitrogen blowing. Thereafter, the chip is set on a samplestage for SEM observation, and an accelerating voltage of 10 kV isapplied, and the silica particle is observed at a magnification of100000× to take an image. From the image taken, 20 silica particles arearbitrarily selected, and the mean of the particle diameters of theparticles is used as the average particle diameter. Here, when a silicaparticle selected has a shape illustrated in FIG. 2, a rectanglepositioned in a manner such that the rectangle is circumscribed aboutthe silica particle 2 and the long side is maximized (circumscribedrectangle L) is derived. The long side and short side of thecircumscribed rectangle L are defined as X and Y, respectively, and thebiaxial average primary particle diameter is calculated as (X+Y)/2,which is used as the particle diameter of the particle.

The size of the pore 3 in the aerogel composite powder will be describedin the section [Density and porosity] described later.

The content of the aerogel component comprised in the aerogel compositepowder can be 4 parts by mass or more, and may be 10 parts by mass ormore, with respect to 100 parts by mass of the total amount of theaerogel composite powder. The content can be 25 parts by mass or less,and may be 20 parts by mass or less. In other words, the content can be4 to 25 parts by mass, and may be 10 to 20 parts by mass. It becomeseasier to impart moderate strength by setting the content to 4 parts bymass or more, and it becomes easier to obtain better thermal insulationby setting the content to 25 parts by mass or less.

The content of the silica particle comprised in the aerogel compositepowder can be 1 part by mass or more, and may be 3 parts by mass ormore, with respect to 100 parts by mass of the total amount of theaerogel composite powder. The content can be 25 parts by mass or less,and may be 15 parts by mass or less. In other words, the content can be1 to 25 parts by mass, and may be 3 to 15 parts by mass. It becomeseasier to impart moderate strength to the aerogel composite by settingthe content to 1 part by mass or more, and it becomes easier to suppressthe solid thermal conduction of the silica particle by setting thecontent to 25 parts by mass or less.

For the purpose of suppressing radiation of heat rays, the aerogelcomposite powder may further comprise an additional component such ascarbon graphite, an aluminum compound, a magnesium compound, a silvercompound, and a titanium compound, in addition to the aerogel componentand the silica particle. The content of the additional component is notlimited in any way, and can be 1 to 5 parts by mass with respect to 100parts by mass of the total amount of the aerogel composite powder tosufficiently ensure desired effects of the aerogel composite.

[Thermal Conductivity]

Because it is difficult to measure the thermal conductivity of a powder,the thermal conductivity of the aerogel composite powder in the presentembodiments is determined through measurement of the thermalconductivity of an aerogel composite block before crushing, which isdescribed later. The thermal conductivity under the atmospheric pressureat 25° C. can be 0.03 W/(m·K) or lower, and may be 0.025 W/(m·K) orlower or 0.02 W/(m·K) or lower. Thermal insulation equal to or higherthan that of polyurethane foam, a high-performance heat insulator, canbe obtained by setting the thermal conductivity to 0.03 W/m·K or lower.The lower limit of the thermal conductivity is not limited in any way,and can be, for example, 0.01 W/m·K.

The thermal conductivity can be measured in accordance with a steadystate method. Specifically, the thermal conductivity can be measured,for example, by using the thermal conductivity analyzer based on asteady state method “HFM 436 Lambda” (produced by NETZSCH, product name,HFM 436 Lambda is a registered trademark). Summary of a method formeasuring the thermal conductivity by using the thermal conductivityanalyzer based on a steady state method is as follows.

(Preparation of Measurement Sample)

The aerogel composite block is processed into a piece in a size of150×150×100 mm³ by using a blade with a blade angle of approximately 20to 25 degrees, and the piece is used as a measurement sample. Here, thethermal conductivity measured with the sample size has been alreadyconfirmed to be almost the same as the thermal conductivity measuredwith the recommended sample size for the HFM 436 Lambda, 300×300×100mm³. Subsequently, the measurement sample is shaped with a sand paper of#1500 or finer to thoroughly smooth the surface, as necessary. Beforemeasurement of thermal conductivity, the measurement sample is dried byusing the thermostatic dryer “DVS402” (produced by Yamato ScientificCo., Ltd., product name) under the atmospheric pressure at 100° C. for30 minutes. The measurement sample is then transferred into a desiccatorand cooled to 25° C. Thus, a measurement sample for measurement of thethermal conductivity is obtained.

(Measurement Method)

Measurement conditions are set such that measurement is performed underthe atmospheric pressure at an average temperature of 25° C. Themeasurement sample obtained as described above is sandwiched between anupper heater and a lower heater with a load of 0.3 MPa, the temperaturedifference, ΔT, is set to 20° C., and the upper surface temperature,lower surface temperature, and so on of the measurement sample aremeasured while the heat flow is adjusted to a one-dimensional heat flowby using a guard heater. The thermal resistance, R_(S), of themeasurement sample is determined by using the following equation:R _(S) =N((T _(U) −T _(L))/Q)−R _(O)wherein T_(U) denotes the upper surface temperature of the measurementsample; T_(L) denotes the lower surface temperature of the measurementsample; R_(O) denotes the contact thermal resistance of the upper/lowerinterface; and Q denotes output from a heat flux meter. N denotes aproportionality coefficient, and is determined in advance by using acalibration sample.

From the thermal resistance, R_(S), obtained, the thermal conductivity,λ, of the measurement sample is determined by using the followingequation:λ=d/R _(S)wherein d denotes the thickness of the measurement sample.

[Compression Modulus]

Because it is difficult to measure the compression modulus of a powder,the compression modulus of the aerogel composite powder in the presentembodiments is determined through measurement of the compression modulusof an aerogel composite block before crushing, which is described later.The compression modulus at 25° C. can be 3 MPa or lower, and may be 2MPa or lower or 1 MPa or lower or 0.5 MPa or lower. It becomes easier toobtain an aerogel composite powder superior in handleability by settingthe compression modulus to 3 MPa or lower. The lower limit of thecompression modulus is not limited in any way, and can be, for example,0.05 MPa.

[Deformation Recovery Rate]

Because it is difficult to measure the deformation recovery rate of apowder, the deformation recovery rate of the aerogel composite powder inthe present embodiments is determined through measurement of thedeformation recovery rate of an aerogel composite block before crushing,which is described later. The deformation recovery rate at 25° C. can be90% or higher, and may be 94% or higher or 98% or higher. It becomeseasier to obtain superior strength, superior flexibility againstdeformation, and the like by setting the deformation recovery rate to90% or higher. The upper limit of the deformation recovery rate is notlimited in any way, and can be, for example, 100% or 99%.

[Maximum Compression Deformation Rate]

Because it is difficult to measure the maximum compression deformationrate of a powder, the maximum compression deformation rate of theaerogel composite powder in the present embodiments is determinedthrough measurement of the maximum compression deformation rate of anaerogel composite block before crushing, which is described later. Themaximum compression deformation rate at 25° C. can be 80% or higher, andmay be 83% or higher or 86% or higher. It becomes easier to obtainsuperior strength, superior flexibility against deformation, and thelike by setting the maximum compression deformation rate to 80% orhigher. The upper limit of the maximum compression deformation rate isnot limited in any way, and can be, for example, 90%.

The compression modulus, deformation recovery rate, and maximumcompression deformation rate can be measured by using the compacttable-top tester “EZ Test” (produced by Shimadzu Corporation, productname). Summary of a method for measuring compression modulus and so onby using the compact table-top tester is as follows.

(Preparation of Measurement Sample)

The aerogel composite block is processed into a cube (dice) of7.0×7.0×7.0 mm by using a blade with a blade angle of approximately 20to 25 degrees, and the cube is used as a measurement sample.Subsequently, the measurement sample is shaped with a sand paper of#1500 or finer to thoroughly smooth the surface, as necessary. Beforemeasurement, the measurement sample is dried by using the thermostaticdryer “DVS402” (produced by Yamato Scientific Co., Ltd., product name)under the atmospheric pressure at 100° C. for 30 minutes. Themeasurement sample is then transferred into a desiccator and cooled to25° C. Thus, a measurement sample for measurement of the compressionmodulus, deformation recovery rate, and maximum compression deformationrate is obtained.

(Measurement Method)

A load cell of 500 N is used. An upper platen (ϕ20 mm) and lower platen(ϕ118 mm) each made of stainless steel are used as jigs for compressionmeasurement. The measurement sample is set between the jigs, andcompressed at a speed of 1 mm/min, and, for example, the change in sizeof the measurement sample at 25° C. is measured. The measurement isterminated at a point of time when a load of higher than 500 N isapplied or when the measurement sample is broken. Here, the compressivestrain, ε, can be determined by using the following equation:ε=Δd/d1wherein Δd denotes the change in thickness (mm) of the measurementsample caused by a load; and d1 denotes the thickness (mm) of themeasurement sample before application of a load.

The compressive stress (MPa), a, can be determined by using thefollowing equation:σ=F/Awherein F denotes compressive force (N); and A denotes thecross-sectional area (mm²) of the measurement sample before applicationof a load.

The compression modulus (MPa), E, can be determined, for example, in arange of compressive force from 0.1 to 0.2 N by using the followingequation:E=(σ₂−σ₁)/(ε₂−ε₁)wherein σ₁ denotes compressive stress (MPa) measured at a compressiveforce of 0.1 N; σ₂ denotes compressive stress (MPa) measured at acompressive force of 0.2 N; ε₁ denotes compressive strain measured at acompressive stress of σ₁; and ε₂ denotes compressive strain measured ata compressive stress of σ₂.

The deformation recovery rate and maximum compression deformation ratecan be determined in accordance with the following equations:Deformation recovery rate=(d3−d2)/(d1−d2)×100Maximum compression deformation rate=(d1−d2)/d1×100wherein d1 denotes the thickness of the measurement sample beforeapplication of a load; d2 denotes the thickness of the measurementsample at a point of time when a load of higher than 500 N is applied orwhen the measurement sample is broken; and d3 denotes the thickness ofthe measurement sample after removal of a load.

The thermal conductivity, compression modulus, deformation recoveryrate, and maximum compression deformation rate can be appropriatelyadjusted, by changing conditions for production or raw materials or thelike of the aerogel composite powder, which are described later.

[Density and Porosity]

The size of the pore 3, namely, the average pore diameter, in theaerogel composite powder in the present embodiments can be 5 to 1000 nm,and may be 25 to 500 nm. It becomes easier to obtain an aerogelcomposite powder superior in flexibility by setting the average porediameter to 5 nm or larger, and it becomes easier to obtain an aerogelcomposite powder superior in thermal insulation by setting the averagepore diameter to 1000 nm or smaller.

The density of the aerogel composite powder in the present embodimentsat 25° C. can be 0.05 to 0.25 g/cm³, and may be 0.1 to 0.2 g/cm³. Moresuperior strength and flexibility can be obtained by setting the densityto 0.05 g/cm³ or higher, and more superior thermal insulation can beobtained by setting the density to 0.25 g/cm³ or lower.

The porosity of the aerogel composite powder in the present embodimentsat 25° C. can be 85 to 95%, and may be 87 to 93%. More superior thermalinsulation can be obtained by setting the porosity to 85% or higher, andmore superior strength and flexibility can be obtained by setting theporosity to 95% or lower.

The average pore diameter, density, and porosity of the aerogelcomposite powder, with regard to the pore (through-hole) connected as athree-dimensional network, can be measured by using mercury porosimetryin accordance with DIN 66133. As the measurement apparatus, for example,an AutoPore IV9520 (produced by Shimadzu Corporation, product name) canbe used.

[Shape of Powder]

The shape of the aerogel composite powder in the present embodiments isnot limited in any way, and may be any of various shapes. Since theaerogel composite powder in the present embodiments has been crushed forpowdering, as described later, the shape of the powder is typically anirregular shape with unevenness in the surface. Needless to say, theshape of the powder may be, for example, spherical. Alternatively, theshape of the powder may be in the form of a panel, a flake, or a fiber.The shape of the powder can be determined through direct observation ofthe aerogel composite powder by using SEM.

[Average Particle Diameter of Powder]

The average particle diameter D50 of the aerogel composite powder in thepresent embodiments can be 1 to 1000 μm, and may be 3 to 700 μm or 5 to500 μm. It becomes easier to obtain an aerogel composite powder superiorin dispersibility, handleability, and so on by setting the averageparticle diameter D50 of the aerogel composite powder to 1 μm or larger.On the other hand, it becomes easier to obtain an aerogel compositepowder superior in dispersibility by setting the average particlediameter D50 to 1000 μm or smaller. The average particle diameter of thepowder can be appropriately adjusted through the crushing method andconditions for crushing, and the manner of sieving, classification, orthe like.

The average particle diameter D50 of the powder can be measured by usinga laser diffraction/scattering method. For example, the aerogelcomposite powder is added to a solvent (ethanol) to a concentration inthe range of 0.05 to 5% by mass, and the resultant is vibrated with a 50W ultrasonic homogenizer for 15 to 30 minutes to disperse the powder.Thereafter, approximately 10 mL of the dispersion is injected into alaser diffraction/scattering particle size distribution analyzer, andthe particle diameter is measured at 25° C. with a refractive index of1.3 and absorption of 0. And then, a particle diameter at 50% of thecumulative value (volume-based) in the particle size distribution isused as the average particle diameter, D50. For the measurementapparatus, for example, a Microtrac MT3000 (produced by Nikkiso Co.,Ltd., product name) can be used.

<Specific Modes of Aerogel Component>

The aerogel composite powder in the present embodiments can comprisepolysiloxane having a main chain including siloxane bonds (Si—O—Si). Theaerogel composite can include, as a structural unit, the following unitM, unit D, unit T, or unit Q.

In the formulas, R represents an atom (e.g., hydrogen atom) or atomgroup (e.g., alkyl group) bonding to a silicon atom. The unit M is aunit consisting of a monovalent group in which a silicon atom is bondingto one oxygen atom. The unit D is a unit consisting of a divalent groupin which a silicon atom is bonding to two oxygen atoms. The unit T is aunit consisting of a trivalent group in which a silicon atom is bondingto three oxygen atoms. The unit Q is a unit consisting of a tetravalentgroup in which a silicon atom is bonding to four oxygen atoms.Information on the contents of these units can be acquired throughSi-NMR.

Examples of the aerogel component of the aerogel composite powder in thepresent embodiments include modes described below. Use of any of thesemodes facilitates control of the thermal insulation and flexibility ofthe aerogel composite powder to desired levels. However, use of any ofthese modes is not necessarily intended to obtain the aerogel compositepowder specified in the present embodiments. By using any of thesemodes, an aerogel composite powder having thermal conductivity andcompression modulus corresponding to the mode can be obtained.Accordingly, an aerogel composite powder having thermal insulation andflexibility suitable for an intended application can be provided.

(First Mode)

The aerogel composite powder in the present embodiments can have astructure represented by the following formula (1). The aerogelcomposite powder in the present embodiments can have a structurerepresented by the following formula (1a), as the structure including astructure represented by the formula (1).

In the formulas (1) and (1a), R¹ and R² each independently represent analkyl group or an aryl group, and R³ and R⁴ each independently representan alkylene group. Here, examples of the aryl group include a phenylgroup and a substituted phenyl group. Examples of the substituent of thesubstituted phenyl group include an alkyl group, a vinyl group, amercapto group, an amino group, a nitro group, and a cyano group. prepresents an integer of 1 to 50. In the formula (1a), two or moregroups as R¹ may be identical or different, and, similarly, two or moregroups as R² may be identical or different. In the formula (1a), two ormore groups as R³ may be identical or different, and, similarly, two ormore groups as R⁴ may be identical or different.

Through introduction of the structure represented by the formula (1) or(1a), as the aerogel component, into the skeleton of the aerogelcomposite powder, the aerogel composite powder is provided with lowthermal conductivity and becomes flexible. From such a viewpoint, R¹ andR² in the formulas (1) and (1a) are, in one example, each independentlyan alkyl group having one to six carbon atoms, a phenyl group, oranother group, and examples of this alkyl group include a methyl group.R³ and R⁴ in the formulas (1) and (1a) are, in one example, eachindependently an alkylene group having one to six carbon atoms oranother group, and examples of this alkylene group include an ethylenegroup and a propylene group. In the formula (1a), p can be 2 to 30, andmay be 5 to 20.

(Second Mode)

The aerogel composite powder in the present embodiments has aladder-type structure including struts and a bridge, wherein the bridgecan have a structure represented by the following formula (2). Throughintroduction of such a ladder-type structure, as the aerogel component,into the skeleton of the aerogel composite powder, the heat resistanceand mechanical strength can be improved. In the present embodiments,“ladder-type structure” is a structure including two struts and bridgeseach connecting the struts (a structure having the form of what iscalled “ladder”). In the present mode, the skeleton of the aerogelcomposite may consist of the ladder-type structure, and the aerogelcomposite powder may partially have the ladder-type structure.

In the formula (2), R⁵ and R⁶ each independently represent an alkylgroup or an aryl group, and b represents an integer of 1 to 50. Here,examples of the aryl group include a phenyl group and a substitutedphenyl group. Examples of the substituent of the substituted phenylgroup include an alkyl group, a vinyl group, a mercapto group, an aminogroup, a nitro group, and a cyano group. When b is an integer of 2 ormore in the formula (2), two or more groups as R⁵ may be identical ordifferent, and, similarly, two or more groups as R⁶ may be identical ordifferent.

Through introduction of the above structure, as the aerogel component,into the skeleton of the aerogel composite powder, for example, theaerogel composite powder is provided with flexibility superior to thatof aerogel having a structure derived from conventional ladder-typesilsesquioxane (i.e., having a structure represented by the followingformula (X)). Silsesquioxane is a polysiloxane having the compositionformula (RSiO_(1.5))_(n), and can have various skeleton structures suchas those of cage-type, ladder-type, and random-type. While the structureof a bridge in aerogel having a structure derived from conventionalladder-type silsesquioxane is —O— (the aerogel includes the above unit Tas a structural unit), as represented by the following formula (X), thestructure of a bridge in the aerogel composite powder in the presentmode is the structure represented by the above formula (2) (polysiloxanestructure). However, the aerogel composite powder in the present modemay have a structure derived from silsesquioxane in addition to thestructure represented by the formula (2).

In the formula (X), R represents a hydroxy group, an alkyl group, or anaryl group.

The structure forming each strut and the chain length thereof, and theinterval in the structure forming bridges are not limited in any way,and the ladder-type structure may be a ladder-type structure representedby the following formula (3) to further improve heat resistance andmechanical strength.

In the formula (3), R⁵, R⁶, R⁷ and R⁸ each independently represent analkyl group or an aryl group; a and c each independently represent aninteger of 1 to 3000; and b represents an integer of 1 to 50. Here,examples of the aryl group include a phenyl group and a substitutedphenyl group. Examples of the substituent of the substituted phenylgroup include an alkyl group, a vinyl group, a mercapto group, an aminogroup, a nitro group, and a cyano group. When b is an integer of 2 ormore in the formula (3), two or more groups as R⁵ may be identical ordifferent, and, similarly, two or more groups as R⁶ may be identical ordifferent. When a is an integer of 2 or more in the formula (3), two ormore groups as R⁷ may be identical or different, and, similarly, when cis an integer of 2 or more, two or more groups as R⁸ may be identical ordifferent.

To obtain more superior flexibility, R⁵, R⁶, R⁷ and R⁸ in the formulas(2) and (3) (R⁷ and R⁸ are only in the formula (3)) are, in one example,each independently an alkyl group having one to six carbon atoms, aphenyl group, or another group, and examples of this alkyl group includea methyl group. In the formula (3), a and c can be each independently 6to 2000, and may be each independently 10 to 1000. In the formulas (2)and (3), b can be 2 to 30, and may be 5 to 20.

(Third Mode)

The aerogel composite powder in the present embodiments may be a driedproduct of a wet gel as a condensate of a sol (a product derived bydrying a wet gel formed from the sol: a dried product of a wet gelderived from the sol) comprising: a silica particle; and at least oneselected from the group consisting of a silicon compound having ahydrolyzable functional group or a condensable functional group (in themolecule) and a hydrolysis product of the silicon compound having ahydrolyzable functional group. Also the aerogel composite describedhereinbefore may be a product derived by drying a wet gel formed from asol comprising a silica particle and a silicon compound or the like asdescribed here.

A silicon compound other than polysiloxane compounds, which aredescribed later, can be used as the silicon compound having ahydrolyzable functional group or a condensable functional group. Inother words, the sol can comprise at least one compound selected fromthe group consisting of a silicon compound having a hydrolyzablefunctional group or a condensable functional group (except polysiloxanecompounds) and a hydrolysis product of the silicon compound having ahydrolyzable functional group (hereinafter, occasionally referred to as“group of silicon compounds”). The number of silicon atoms in themolecule of the silicon compound can be 1 or 2.

The silicon compound having a hydrolyzable functional group is notlimited in any way, and examples thereof include alkylsilicon alkoxide.The number of hydrolyzable functional groups of the alkylsiliconalkoxide can be three or less to improve the water resistance. Examplesof such alkylsilicon alkoxide include monoalkyltrialkoxysilane,monoalkyldialkoxysilane, dialkyldialkoxysilane, monoalkylmonoalkoxysilane, and dialkylmonoalkoxysilane,trialkylmonoalkoxysilane, specifically methyltrimethoxysilane,methyldimethoxysilane, dimethyldimethoxysilane, andethyltrimethoxysilane. Examples of the hydrolyzable functional groupinclude an alkoxy group such as a methoxy group and an ethoxy group.

The silicon compound having a condensable functional group is notlimited in any way, and examples thereof include silanetetraol,methylsilanetriol, dimethylsilanediol, phenylsilanetriol,phenylmethylsilanediol, diphenylsilanediol, n-propylsilanetriol,hexylsilanetriol, octylsilanetriol, decylsilanetriol, andtrifluoropropylsilanetriol.

The silicon compound having a hydrolyzable functional group or acondensable functional group may further have a reactive group differentfrom a hydrolyzable functional group and a condensable functional group(a functional group corresponding to none of hydrolyzable functionalgroups and condensable functional groups). Examples of the reactivegroup include an epoxy group, a mercapto group, a glycidoxy group, avinyl group, an acryloyl group, a methacryloyl group, and an aminogroup. The epoxy group may be included in an epoxy group-containinggroup such as a glycidoxy group.

Also applicable as a silicon compound having a reactive group in whichthe number of hydrolyzable functional groups is three or less are, forexample, vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,3-glycidoxypropylmethyldimethoxysilane,3-methacryloxypropyltrimethoxysilane,3-methacryloxypropylmethyldimethoxysilane,3-acryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane,3-mercaptopropylmethyldimethoxysilane,N-phenyl-3-aminopropyltrimethoxysilane, andN-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane.

Also applicable as a silicon compound having a condensable functionalgroup and a reactive functional group are, for example, vinylsilanetriol, 3-glycidoxypropylsilanetriol,3-glycidoxypropylmethylsilanediol, 3-methacryloxypropylsilanetriol,3-methacryloxypropylmethylsilanediol, 3-acryloxypropylsilanetriol,3-mercaptopropylsilanetriol, 3-mercaptopropylmethylsilanediol,N-phenyl-3-aminopropylsilanetriol, andN-2-(aminoethyl)-3-aminopropylmethylsilanediol.

In addition, bis(trimethoxysilyl)methane, bis(trimethoxysilyl) ethane,bis(trimethoxysilyl)hexane, ethyltrimethoxysilane,vinyltrimethoxysilane, etc., each as a silicon compound in which thenumber of hydrolyzable functional groups at molecular ends is three orless are also applicable.

The silicon compound having a hydrolyzable functional group or acondensable functional group (except polysiloxane compounds) andhydrolysis product of the silicon compound having a hydrolyzablefunctional group may be used singly, or as a mixture of two or more.

In production of the aerogel composite powder in the presentembodiments, the silicon compound can comprise a polysiloxane compoundhaving a hydrolyzable functional group or a condensable functionalgroup. In other words, the sol comprising the silicon compound canfurther comprise at least one selected from the group consisting of apolysiloxane compound having a hydrolyzable functional group or acondensable functional group (in the molecule) and a hydrolysis productof the polysiloxane compound having a hydrolyzable functional group(hereinafter, occasionally referred to as “group of polysiloxanecompounds”).

The functional group of the polysiloxane compound or the like is notlimited in any way, and can be a group reactive with the same functionalgroup or reactive with another functional group. Examples of thehydrolyzable functional group include an alkoxy group. Examples of thecondensable functional group include a hydroxy group, a silanol group, acarboxy group, and a phenolic hydroxy group. The hydroxy group may beincluded in a hydroxy group-containing group such as a hydroxyalkylgroup. The polysiloxane compound having a hydrolyzable functional groupor a condensable functional group may further have the above-describedreactive group different from a hydrolyzable functional group and acondensable functional group (a functional group corresponding to noneof hydrolyzable functional groups and condensable functional groups).The polysiloxane compound having the functional group and reactive groupmay be used singly, or as a mixture of two or more. Examples of thefunctional group and reactive group as a group to improve theflexibility of the aerogel composite include an alkoxy group, a silanolgroup, and hydroxyalkyl group, and the alkoxy group and hydroxyalkylgroup among them can further improve the compatibility of the sol. Forimprovement of the reactivity of the polysiloxane compound and reductionof the thermal conductivity of the aerogel composite powder, the numberof carbon atoms of the alkoxy group or hydroxyalkyl group can be 1 to 6,and may be 2 to 4 for further improvement of the flexibility of theaerogel composite powder.

Examples of the polysiloxane compound having a hydroxyalkyl groupinclude those having a structure represented by the following formula(A). By using the polysiloxane compound having a structure representedby the following formula (A), the structures represented by the aboveformulas (1) and (1a) can be introduced into the skeleton of the aerogelcomposite powder.

In the formula (A), R^(1a) represents a hydroxyalkyl group; R^(2a)represents an alkylene group; R^(3a) and R^(4a) each independentlyrepresent an alkyl group or an aryl group; and n represents an integerof 1 to 50. Here, examples of the aryl group include a phenyl group anda substituted phenyl group. Examples of the substituent of thesubstituted phenyl group include an alkyl group, a vinyl group, amercapto group, an amino group, a nitro group, and a cyano group. In theformula (A), two groups as R^(1a) may be identical or different, and,similarly, two groups as R^(2a) may be identical or different. In theformula (A), two or more groups as R^(3a) may be identical or different,and, similarly, two or more groups as R^(4a) may be identical ordifferent.

It becomes much easier to obtain an aerogel composite powder having lowthermal conductivity and being flexible by using a wet gel as acondensate of the sol (or formed from the sol) comprising thepolysiloxane compound having the above structure. From such a viewpoint,R^(1a) in the formula (A) is, in one example, a hydroxyalkyl grouphaving one to six carbon atoms, and examples of this hydroxyalkyl groupinclude a hydroxyethyl group and a hydroxypropyl group. R^(2a) in theformula (A) is, in one example, an alkylene group having one to sixcarbon atoms, and examples of this alkylene group include an ethylenegroup and a propylene group. R^(3a) and R^(4a) in the formula (A) are,in one example, each independently an alkyl group having one to sixcarbon atoms, a phenyl group, or another group, and examples of thisalkyl group include a methyl group. In the formula (A), n can be 2 to30, and may be 5 to 20.

A commercially available product can be used as the polysiloxanecompound having the structure represented by the above formula (A), andexamples thereof include compounds including X-22-160AS, KF-6001,KF-6002, and KF-6003 (all produced by Shin-Etsu Chemical Co., Ltd.) andcompounds including XF42-B0970 and Fluid OFOH 702-4% (all produced byMomentive Performance Materials Inc.).

Examples of the polysiloxane compound having an alkoxy group includethose having a structure represented by the following formula (B). Byusing the polysiloxane compound having a structure represented by thefollowing formula (B), the ladder-type structure with bridgesrepresented by the above formula (2) can be introduced into the skeletonof the aerogel composite powder.

In the formula (B), R^(1b) represents an alkyl group, an alkoxy group,or an aryl group; R^(2b) and R^(3b) each independently represent analkoxy group; R^(4b) and R^(5b) each independently represent an alkylgroup or an aryl group; and m represents an integer of 1 to 50. Here,examples of the aryl group include a phenyl group and a substitutedphenyl group. Examples of the substituent of the substituted phenylgroup include an alkyl group, a vinyl group, a mercapto group, an aminogroup, a nitro group, and a cyano group. In the formula (B), two groupsas R^(1b) may be identical or different, two groups as R^(2b) may beidentical or different, and, similarly, two groups as R^(3b) may beidentical or different. When m is an integer of 2 or more in the formula(B), two or more groups as R^(4b) may be identical or different, and,similarly, two or more groups as R^(5b) may be identical or different.

It becomes much easier to obtain an aerogel composite powder having lowthermal conductivity and being flexible by using a wet gel as acondensate of the sol (or formed from the sol) comprising thepolysiloxane compound having the above structure or a hydrolysis productthereof. From such a viewpoint, R^(1b) in the formula (B) is, in oneexample, an alkyl group having one to six carbon atoms or an alkoxygroup having one to six carbon atoms, and examples of this alkyl groupor alkoxy group include a methyl group, a methoxy group, and an ethoxygroup. R^(2b) and R^(3b) in the formula (B) are, in one example, eachindependently an alkoxy group having one to six carbon atoms, andexamples of this alkoxy group include a methoxy group and an ethoxygroup. R^(4b) and R^(5b) in the formula (B) are, in one example, eachindependently an alkyl group having one to six carbon atoms, a phenylgroup, or another group, and examples of this alkyl group include amethyl group. In the formula (B), m can be 2 to 30, and may be 5 to 20.

The polysiloxane compound having the structure represented by the aboveformula (B) can be obtained appropriately with reference, for example,to any of production methods reported in Japanese Unexamined PatentPublication No. 2000-26609 and Japanese Unexamined Patent PublicationNo. 2012-233110.

Since an alkoxy group is hydrolyzable, the polysiloxane compound havingan alkoxy group is possibly present as a hydrolysis product in the sol,and the polysiloxane compound having an alkoxy group and a hydrolysisproduct thereof may coexist. In the polysiloxane compound having analkoxy group, alkoxy groups in the molecule may be totally hydrolyzed orpartially hydrolyzed.

The polysiloxane compound having a hydrolyzable functional group or acondensable functional group and hydrolysis product of the polysiloxanecompound having a hydrolyzable functional group may be used singly, oras a mixture of two or more.

The content of the group of silicon compounds (the sum total of thecontent of the silicon compound having a hydrolyzable functional groupor a condensable functional group and the content of the hydrolysisproduct of the silicon compound having a hydrolyzable functional group)comprised in the sol can be 5 parts by mass or more, and may be 10 partsby mass or more, with respect to 100 parts by mass of the total amountof the sol. The content can be 50 parts by mass or less, and may be 30parts by mass or less, with respect to 100 parts by mass of the totalamount of the sol. In other words, the content of the group of siliconcompounds can be 5 to 50 parts by mass, and may be 10 to 30 parts bymass, with respect to 100 parts by mass of the total amount of the sol.It becomes easier to obtain better reactivity by setting the content to5 parts by mass or more, and it becomes easier to obtain bettercompatibility by setting the content to 50 parts by mass or less.

When the sol further comprises the polysiloxane compound, the sum totalof the content of the group of silicon compounds and the content of thegroup of polysiloxane compounds (the sum total of the content of thepolysiloxane compound having a hydrolyzable functional group or acondensable functional group and the content of the hydrolysis productof the polysiloxane compound having a hydrolyzable functional group) canbe 5 parts by mass or more, and may be 10 parts by mass or more, withrespect to 100 parts by mass of the total amount of the sol. The sumtotal of the contents can be 50 parts by mass or less, and may be 30parts by mass or less, with respect to 100 parts by mass of the totalamount of the sol. In other words, the sum total of the contents can be5 to 50 parts by mass, and may be 10 to 30 parts by mass, with respectto 100 parts by mass of the total amount of the sol. It becomes mucheasier to obtain better reactivity by setting the sum total of thecontents to 5 parts by mass or more, and it becomes much easier toobtain better compatibility by setting the sum total of the contents to50 parts by mass or less. In this case, the ratio of the content of thegroup of silicon compounds to the content of the group of polysiloxanecompounds can be 0.5:1 to 4:1, and may be 1:1 to 2:1. It becomes mucheasier to obtain better compatibility by setting the ratio of thecontents of these compounds to 0.5:1 or higher, and it becomes mucheasier to prevent the gel from shrinking by setting the ratio of thecontents of these compounds to 4:1 or lower.

The content of the silica particle comprised in the sol can be 1 part bymass or more, and may be 4 parts by mass or more, with respect to 100parts by mass of the total amount of the sol. The content can be 20parts by mass or less, and may be 15 parts by mass or less, with respectto 100 parts by mass of the total amount of the sol. In other words, thecontent of the silica particle can be 1 to 20 parts by mass, and may be4 to 15 parts by mass, with respect to 100 parts by mass of the totalamount of the sol. It becomes easier to impart moderate strength toaerogel and obtain an aerogel composite powder superior in shrinkageresistance in drying by setting the content to 1 part by mass or more.It becomes easier to suppress the solid thermal conduction of the silicaparticle and obtain an aerogel composite powder superior in thermalinsulation by setting the content to 20 parts by mass or less.

(Other Modes)

The aerogel composite powder in the present embodiments can have astructure represented by the following formula (4). The aerogelcomposite powder in the present embodiments can comprise the silicaparticle and simultaneously have a structure represented by thefollowing formula (4).

In the formula (4), R⁹ represents an alkyl group. Examples of the alkylgroup include an alkyl group having one to six carbon atoms, andexamples of this alkyl group include a methyl group.

The aerogel composite powder in the present embodiments can have astructure represented by the following formula (5). The aerogelcomposite powder in the present embodiments can comprise the silicaparticle and simultaneously have a structure represented by thefollowing formula (5).

In the formula (5), R¹⁰ and R¹¹ each independently represent an alkylgroup. Here, examples of the alkyl group include an alkyl group havingone to six carbon atoms, and examples of this alkyl group include amethyl group.

The aerogel composite powder in the present embodiments can have astructure represented by the following formula (6). The aerogelcomposite powder in the present embodiments can comprise the silicaparticle and simultaneously have a structure represented by thefollowing formula (6).

In the formula (6), R¹² represents an alkylene group. Here, examples ofthe alkylene group include an alkylene group having 1 to 10 carbonatoms, and examples of this alkylene group include an ethylene group anda hexylene group.

<Method for Producing Aerogel Composite Powder>

Next, the method for producing an aerogel composite powder will bedescribed. The method for producing an aerogel composite powder is notlimited in any way, and an aerogel composite can be produced, forexample, by using the following method.

Specifically, the aerogel composite powder in the present embodimentscan be produced by using a production method primarily including: a stepof forming a sol; a step of forming a wet gel, where the sol obtained inthe step of forming a sol is gelled and then aged to obtain a wet gel; astep of washing and solvent displacement, where the wet gel obtained inthe step of forming a wet gel is washed and subjected to solventdisplacement (as necessary); a step of drying, where the wet gel washedand subjected to solvent displacement is dried; and a step of crushing ablock, where an aerogel composite block obtained by drying is crushed.

Alternatively, the aerogel composite powder in the present embodimentscan be produced by using a production method primarily including: a stepof forming a sol; the step of forming a wet gel; a step of crushing awet gel, where the wet gel obtained in the step of forming a wet gel iscrushed; the step of washing and solvent displacement; and the step ofdrying.

The size of the aerogel composite powder obtained can be furtherhomogenized by sieving, classification, or the like. If the size of thepowder is uniformed, the handleability can be enhanced. “Sol” refers toa state before the occurrence of gelling reaction, and, in the presentembodiments, a state in which the group of silicon compounds, optionallywith the group of polysiloxane compounds, and the silica particle aredissolved or dispersed in a solvent. Wet gel refers to a gel solid in awet state which contains a liquid medium but does not have fluidity.

Now, each step of the method for producing the aerogel composite powderin the present embodiments will be described.

(Step of Forming Sol)

The step of forming a sol is a step in which the above-described siliconcompound, optionally with the polysiloxane compound, and the silicaparticle or a solvent containing the silica particle are mixed togetherfor hydrolysis to form the sol. In this step, an acid catalyst may befurther added into the solvent to accelerate hydrolysis reaction. Asshown in Japanese Patent No. 5250900, a surfactant, athermally-hydrolyzable compound, etc., can be added into the solvent.Moreover, a component such as carbon graphite, an aluminum compound, amagnesium compound, a silver compound, and a titanium compound may beadded into the solvent, for example, for the purpose of suppressingradiation of heat rays.

For example, water or a mixed solution of water and an alcohol can beused as the solvent. Examples of the alcohol include methanol, ethanol,n-propanol, 2-propanol, n-butanol, 2-butanol, and t-butanol. Among them,alcohols with a low surface tension and low boiling point for reductionof the interfacial tension on a gel wall are, for example, methanol,ethanol, and 2-propanol. These may be used singly, or as a mixture oftwo or more thereof.

If an alcohol is used as the solvent, for example, the amount of thealcohol can be 4 to 8 mol, and may be 4 to 6.5 mol or 4.5 to 6 mol, withrespect to 1 mol of the total amount of the group of silicon compoundsand the group of polysiloxane compounds. It becomes much easier toobtain better compatibility by setting the amount of the alcohol to 4mol or more, and it becomes much easier to prevent the gel fromshrinking by setting the amount of the alcohol to 8 mol or less.

Examples of the acid catalyst include inorganic acids such ashydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid,sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid,bromic acid, chloric acid, chlorous acid, and hypochlorous acid; acidicphosphates such as acidic aluminum phosphate, acidic magnesiumphosphate, and acidic zinc phosphate; and organic carboxylic acids suchas acetic acid, formic acid, propionic acid, oxalic acid, malonic acid,succinic acid, citric acid, malic acid, adipic acid, and azelaic acid.Among them, acid catalysts to further improve the water resistance of anaerogel composite to be obtained are, for example, organic carboxylicacids. Examples of such organic carboxylic acids include acetic acid;however, formic acid, propionic acid, oxalic acid, malonic acid, and soon are also acceptable. These may be used singly, or as a mixture of twoor more thereof.

By using the acid catalyst, hydrolysis reaction of the silicon compoundand the polysiloxane compound can be accelerated and the sol can beobtained in a shorter period of time.

The amount of the acid catalyst to be added can be 0.001 to 0.1 parts bymass with respect to 100 parts by mass of the total amount of the groupof silicon compounds and the group of polysiloxane compounds.

For the surfactant, nonionic surfactant, ionic surfactant, or the likecan be used. These may be used singly, or as a mixture of two or morethereof.

For the nonionic surfactant, for example, a compound including ahydrophilic moiety such as polyoxyethylene and a hydrophobic moietyprimarily consisting of an alkyl group or a compound including ahydrophilic moiety such as polyoxypropylene can be used. Examples of thecompound including a hydrophilic moiety such as polyoxyethylene and ahydrophobic moiety primarily consisting of an alkyl group includepolyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether,and polyoxyethylene alkyl ether. Examples of the compound including ahydrophilic moiety such as polyoxypropylene include polyoxypropylenealkyl ether and a block copolymer of polyoxyethylene andpolyoxypropylene.

Examples of the ionic surfactant include cationic surfactant, anionicsurfactant, and amphoteric surfactant. Examples of the cationicsurfactant include cetyltrimethylammonium bromide andcetyltrimethylammonium chloride, and examples of the anionic surfactantinclude sodium dodecylsulfonate. Examples of the amphoteric surfactantinclude amino acid-based surfactant, betaine-based surfactant, and amineoxide-based surfactant. Examples of the amino acid-based surfactantinclude acylglutamic acid. Examples of the betaine-based surfactantinclude betaine lauryldimethylaminoacetate and betainestearyldimethylaminoacetate. Examples of the amine oxide-basedsurfactant include lauryldimethylamine oxide.

In the step of forming a wet gel, which is described later, thesesurfactants are inferred to act to reduce the difference in chemicalaffinity between a solvent and a growing siloxane polymer in thereaction system, and thereby prevent phase separation.

The amount of the surfactant to be added can be, for example, 1 to 100parts by mass with respect to 100 parts by mass of the total amount ofthe group of silicon compounds and the group of polysiloxane compounds,although it depends on the type of the surfactant and the types andamounts of the group of silicon compounds and the group of polysiloxanecompounds. The amount to be added may be 5 to 60 parts by mass.

The thermally-hydrolyzable compound is inferred to generate a basecatalyst through thermal hydrolysis to basify the reaction solution, andaccelerate sol-gel reaction in the step of forming a wet gel, which isdescribed later. Hence, the thermally-hydrolyzable compound is notlimited in any way as long as it is a compound capable of basifying thereaction solution after hydrolysis, and examples thereof include urea;acid amide such as formamide, N-methylformamide, N,N-dimethylformamide,acetamide, N-methylacetamide, and N,N-dimethylacetamide; and cyclicnitrogen compounds such as hexamethylenetetramine Among them, ureaparticularly satisfactorily provides the above accelerating effect.

The amount of the thermally-hydrolyzable compound to be added is notlimited in any way as long as it is an amount such that sol-gel reactioncan be sufficiently accelerated in the step of forming a wet gel, whichis described later. When urea is used as the thermally-hydrolyzablecompound, for example, the amount of urea to be added can be 1 to 200parts by mass with respect to 100 parts by mass of the total amount ofthe group of silicon compounds and the group of polysiloxane compounds.The amount to be added may be 2 to 150 parts by mass. It becomes mucheasier to obtain good reactivity by setting the amount to be added to 1part by mass or more, and it becomes much easier to preventprecipitation of crystals and lowering of gel density by setting theamount to be added to 200 parts by mass or less.

Hydrolysis in the step of forming a sol may be performed, for example,in a temperature environment of 20 to 60° C. for 10 minutes to 24 hours,and may be performed in a temperature environment of 50 to 60° C. for 5minutes to 8 hours, although the conditions depend on the types andamounts of the silicon compound, polysiloxane compound, silica particle,acid catalyst, surfactant, etc., in the mixed solution. Thereby, thehydrolyzable functional groups in the silicon compound and polysiloxanecompound are sufficiently hydrolyzed, and hence a hydrolysis product ofthe silicon compound and a hydrolysis product of the polysiloxanecompound can be obtained more reliably.

When the thermally-hydrolyzable compound is added into the solvent,however, the temperature environment in the step of forming a sol may becontrolled to a temperature such that the hydrolysis of thethermally-hydrolyzable compound is inhibited to prevent the sol fromgelling. The temperature in this case may be any temperature such thatthe hydrolysis of the thermally-hydrolyzable compound can be inhibited.When urea is used as the thermally-hydrolyzable compound, for example,the temperature environment in the step of forming a sol can be 0 to 40°C., and may be 10 to 30° C.

(Step of Forming Wet Gel)

The step of forming a wet gel is a step in which the sol obtained in thestep of forming a sol is gelled and then aged to obtain a wet gel. Inthis step, a base catalyst can be used to accelerate gelling.

Examples of the base catalyst include alkali metal hydroxides such aslithium hydroxide, sodium hydroxide, potassium hydroxide, and cesiumhydroxide; ammonium compounds such as ammonium hydroxide, ammoniumfluoride, ammonium chloride, and ammonium bromide; basic sodiumphosphate such as sodium metaphosphate, sodium pyrophosphate, and sodiumpolyphosphate; aliphatic amines such as allylamine, diallylamine,triallylamine, isopropylamine, diisopropylamine, ethylamine,diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine,diisobutylamine, 3-(diethylamino)propylamine, di-2-ethylhexylamine,3-(dibutylamino)propylamine, tetramethylethylenediamine, t-butylamine,sec-butylamine, propylamine, 3-(methylamino)propylamine,3-(dimethylamino)propyl amine, 3-methoxyamine, dimethylethanolamine,methyldiethanolamine, diethanolamine, and triethanolamine;nitrogen-containing heterocyclic compounds such as morpholine,N-methylmorpholine, 2-methylmorpholine, piperazine and derivativesthereof, piperidine and derivatives thereof, and imidazole andderivatives thereof. Among them, ammonium hydroxide (aqueous ammonia) issuperior in that, as well as superiority in economic efficiency, it hashigh volatility and is less likely to remain in the aerogel compositepowder after drying, and hence hardly deteriorates the water resistance.These base catalysts may be used singly, or as a mixture of two or morethereof.

By using the base catalyst, dehydration condensation reaction ordealcoholization condensation reaction of the silicon compound,polysiloxane compound, and silica particle in the sol can be acceleratedto complete the gelling of the sol in a shorter period of time. Thereby,a wet gel with higher strength (rigidity) can be obtained. Inparticular, ammonia has high volatility and is less likely to remain inthe aerogel composite powder, and hence an aerogel composite powder moresuperior in water resistance can be obtained by using ammonia as thebase catalyst.

The amount of the base catalyst to be added can be 0.5 to 5 parts bymass, and may be 1 to 4 parts by mass, with respect to 100 parts by massof the total amount of the group of silicon compounds and the group ofpolysiloxane compounds. Gelling can be completed in a shorter period oftime by setting the amount of the base catalyst to be added to 0.5 partsby mass or more, and lowering of the water resistance can be morereduced by setting the amount to 5 parts by mass or less.

Gelling of the sol in the step of forming a wet gel may be performed inan airtight container so as not to allow the solvent and base catalystto volatile. The gelling temperature can be 30 to 90° C., and may be 40to 80° C. Gelling can be completed in a shorter period of time and a wetgel with higher strength (rigidity) can be obtained by setting thegelling temperature to 30° C. or higher. It becomes easier to suppressthe volatilization of the solvent (in particular, an alcohol) by settingthe gelling temperature to 90° C. or lower, and hence gelling can becompleted while volume shrinkage is prevented.

Aging in the step of forming a wet gel may be performed in an airtightcontainer so as not to allow the solvent and base catalyst to volatize.Aging strengthens the bonding of the components constituting a wet gel,and as a result a wet gel with sufficiently high strength (rigidity) forpreventing shrinkage in drying can be obtained. The aging temperaturecan be 30 to 90° C., and may be 40 to 80° C. A wet gel with higherstrength (rigidity) can be obtained by setting the aging temperature to30° C. or higher, and it becomes easier to suppress the volatilizationof the solvent (in particular, an alcohol) by setting the agingtemperature to 90° C. or lower, and hence gelling can be completed whilevolume shrinkage is prevented.

It is often difficult to determine when the gelling of the sol iscompleted, and hence gelling and subsequent aging of the sol may besequentially performed in a series of operations.

The gelling time and aging time depend on the gelling temperature andaging temperature; however, the silica particle is comprised in the solin the present embodiments, and as a result, in particular, the gellingtime can be reduced as compared with conventional methods for producingaerogel. The reason is presumably that silanol groups or reactive groupspossessed by the silicon compound, polysiloxane compound, etc., in thesol form hydrogen bonding or chemical bonding with silanol groups of thesilica particle. The gelling time can be 10 to 120 minutes, and may be20 to 90 minutes. It becomes easier to obtain a more homogeneous wet gelby setting the gelling time to 10 minutes or longer, and the steps fromthe step of washing and solvent displacement to the step of drying,which are described later, can be simplified by setting the gelling timeto 120 minutes or shorter. The total time of the gelling time and agingtime, as a total of the step of gelling and aging, can be 4 to 480hours, and may be 6 to 120 hours. A wet gel with higher strength(rigidity) can be obtained by setting the total of the gelling time andaging time to 4 hours or longer, and it becomes easier to maintain theeffect of aging by setting the total of the gelling time and aging timeto 480 hours or shorter.

To impart a lower density or a larger average pore diameter to anaerogel composite powder to be obtained, the gelling temperature andaging temperature may be raised within the above range or the total timeof the gelling time and aging time may be prolonged within the aboverange. Alternatively, to impart a higher density or a smaller averagepore diameter to an aerogel composite powder to be obtained, the gellingtemperature and aging temperature may be lowered within the above rangeor the total time of the gelling time and aging time may be shortenedwithin the above range.

(Step of Crushing Wet Gel)

When the step of crushing a wet gel is performed, the wet gel obtainedin the step of forming a wet gel is crushed. For crushing, for example,the wet gel is placed in a Henschel mixer or the step of forming a wetgel is performed in a mixer, and the mixer is operated under moderateconditions (rotational frequency and duration). For crushing, moresimply, the wet gel is placed in a sealable container or the step offorming a wet gel is performed in a sealable container, and the wet gelis shaken for a moderate duration with a shaking apparatus such as ashaker. As necessary, the particle diameter of the wet gel can beadjusted by using, a jet mill, a roller mill, a bead mill, or the like.

(Step of Washing and Solvent Displacement)

The step of washing and solvent displacement is a step including asubstep of washing the wet gel obtained in the step of forming a wet gelor the step of crushing a wet gel (a substep of washing) and a substepof displacing the washing solution in the wet gel with a solventsuitable for conditions for drying (in the step of drying describedlater) (a substep of solvent displacement). Although the step of washingand solvent displacement can be performed in a manner such that thesubstep of washing the wet gel is not performed and only the substep ofsolvent displacement is performed, the wet gel may be washed to reduceimpurities including unreacted matters and byproducts in the wet gel andenable production of an aerogel composite powder having higher purity.In the present embodiments, the substep of solvent displacement afterthe substep of washing is not necessarily essential, as described later,because the silica particle is comprised in the gel.

In the substep of washing, the wet gel obtained in the step of forming awet gel or the step of crushing a wet gel is washed. This washing can beperformed repeatedly, for example, by using water or an organic solvent.In washing, the washing efficiency can be improved by heating.

For the organic solvent, various organic solvents can be used, such asmethanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, methylethyl ketone, 1,2-dimethoxyethane, acetonitrile, hexane, toluene,diethyl ether, chloroform, ethyl acetate, tetrahydrofuran, methylenechloride, N,N-dimethylformamide, dimethylsulfoxide, acetic acid, andformic acid. These organic solvents may be used singly, or as a mixtureof two or more thereof.

In the substep of solvent displacement, which is described later, asolvent with low surface tension can be used to prevent the gel fromshrinking due to drying. However, solvents with low surface tensiongenerally have extremely low mutual solubility with water. For thisreason, the organic solvent used for the substep of washing when asolvent with low surface tension is used in the substep of solventdisplacement is, for example, a hydrophilic organic solvent having highmutual solubility with both water and the solvent with low surfacetension. The hydrophilic organic solvent used in the substep of washingcan serve for pre-displacement for the substep of solvent displacement.Examples of the hydrophilic organic solvent include, among the aboveorganic solvents, methanol, ethanol, 2-propanol, acetone, and methylethyl ketone. Methanol, ethanol, methyl ethyl ketone, etc., are superiorin economic efficiency.

The amount of water or the organic solvent used in the substep ofwashing can be an amount such that the solvent in the wet gel can besufficiently displaced and washed out. The amount can be 3 to 10 timesthe volume of the wet gel. Washing can be repeated until the moisturecontent of the wet gel after washing reaches 10% by mass or less to themass of silica.

The temperature environment in the substep of washing can be atemperature equal to or lower than the boiling point of the solvent usedfor washing, and, when methanol is used, for example, heating can beperformed at a temperature of around 30 to 60° C.

In the substep of solvent displacement, the solvent of the wet gelwashed is displaced with a specific solvent for displacement to preventshrinkage in the step of drying, which is described later. Then, theefficiency of displacement can be improved by heating. Specifically,when drying is performed under the atmospheric pressure at a temperaturelower than the critical point of the solvent used in drying in the stepof drying, the solvent for displacement is, for example, a solvent withlow surface tension, which is described later. When supercritical dryingis performed, on the other hand, the solvent for displacement is, forexample, ethanol, methanol, 2-propanol, dichlorodifluoromethane, carbondioxide, or a mixed solvent of two or more of them.

Examples of the solvent with low surface tension include solvents with asurface tension of 30 mN/m or lower at 20° C. The surface tension may be25 mN/m or lower or 20 mN/m or lower. Examples of the solvent with lowsurface tension include aliphatic hydrocarbons such as pentane (15.5),hexane (18.4), heptane (20.2), octane (21.7), 2-methylpentane (17.4),3-methylpentane (18.1), 2-methylhexane (19.3), cyclopentane (22.6),cyclohexane (25.2), and 1-pentene (16.0); aromatic hydrocarbons such asbenzene (28.9), toluene (28.5), m-xylene (28.7), and p-xylene (28.3);halogenated hydrocarbons such as dichloromethane (27.9), chloroform(27.2), carbon tetrachloride (26.9), 1-chloropropane (21.8), and2-chloropropane (18.1); ethers such as ethyl ether (17.1), propyl ether(20.5), isopropyl ether (17.7), butyl ethyl ether (20.8), and1,2-dimethoxyethane (24.6); ketones such as acetone (23.3), methyl ethylketone (24.6), methyl propyl ketone (25.1), and diethyl ketone (25.3);and esters such as methyl acetate (24.8), ethyl acetate (23.8), propylacetate (24.3), isopropyl acetate (21.2), isobutyl acetate (23.7), andethyl butyrate (24.6), where a numerical value in each parenthesisindicates surface tension at 20° C., and the unit is [mN/m]. Among them,aliphatic hydrocarbons (e.g., hexane, heptane) have low surface tension,and are superior in terms of the working environment. In addition,hydrophilic organic solvents among the above solvents, such as acetone,methyl ethyl ketone, and 1,2-dimethoxyethane, can simultaneously serveas the organic solvent for the substep of washing, if used. A solventwith a boiling point of 100° C. or lower at ambient pressure among theabove solvents may be used because of easiness in drying in the step ofdrying, which is described later. The above solvents may be used singly,or as a mixture of two or more thereof.

The amount of the solvent to be used in the substep of solventdisplacement can be an amount such that the solvent in the wet gel afterwashing can be sufficiently displaced. The amount can be 3 to 10 timesthe volume of the wet gel.

The temperature environment in the substep of solvent displacement canbe a temperature equal to or lower than the boiling point of the solventused for displacement, and, when heptane is used, for example, heatingcan be performed at a temperature of around 30 to 60° C.

In the present embodiments, the substep of solvent displacement is notnecessarily essential, as described above, because the silica particleis comprised in the gel. The mechanism is inferred as follows: while thesolvent of the wet gel is, in conventional methods, displaced with aspecific solvent for displacement (a solvent with low surface tension)to prevent shrinkage in the step of drying, the silica particlefunctions as a support for the three-dimensional network skeleton andthe skeleton is supported in the present embodiments, and the shrinkageof the gel in the step of drying is prevented; therefore, the gel can besubjected directly to the step of drying without displacement of thesolvent used in washing. As described above, the steps from the step ofwashing and solvent displacement to the step of drying can be simplifiedin the present embodiments. However, the present embodiments neverexclude implementation of the substep of solvent displacement.

(Step of Drying)

In the step of drying, the wet gel washed and (as necessary) subjectedto solvent displacement as described above is dried. Thereby, an aerogelcomposite block or powder is obtained. That is, an aerogel derived bydrying the wet gel formed from the above sol can be obtained.

The technique for drying is not limited in any way, and known ambientpressure drying, supercritical drying, or freeze drying can be used.Among them, ambient pressure drying or supercritical drying can be usedfor easiness in production of an aerogel composite block or powderhaving low density. To enable production at low cost, ambient pressuredrying can be used. In the present embodiments, ambient pressure refersto 0.1 MPa (atmospheric pressure).

The aerogel composite block or powder can be obtained by drying the wetgel washed and (as necessary) subjected to solvent displacement underthe atmospheric pressure at a temperature lower than the critical pointof the solvent used in drying. The drying temperature, which depends onthe type of the solvent used for displacement (the solvent used inwashing, for the case without solvent displacement), can be 20 to 150°C. in consideration that drying at high temperature particularlyincreases the evaporation rate of the solvent and in some casesgenerates a large crack in the gel. The drying temperature may be 60 to120° C. The drying time depends on the volume of the wet gel and thedrying temperature, and can be 4 to 120 hours. In the presentembodiments, acceleration of drying by applying a pressure lower thanthe critical point in a manner such that the productivity is not loweredis also encompassed in the concept of ambient pressure drying.

Alternatively, the aerogel composite block or powder can be obtained byapplying supercritical drying to the wet gel washed and (as necessary)subjected to solvent displacement. Supercritical drying can be performedby using a known technique. Examples of the method for supercriticaldrying include a method of removing the solvent contained in the wet gelat a temperature and pressure equal to or higher than the critical pointof the solvent. Another example of the method for supercritical dryingis a method in which the wet gel is soaked in liquified carbon dioxide,for example, under conditions of around 20 to 25° C. and 5 to 20 MPa tototally or partially displace the solvent contained in the wet gel withcarbon dioxide, which has a critical point lower than the solvent, andsingle carbon dioxide or a mixture of carbon dioxide and the solvent isthen removed.

The aerogel composite block or powder obtained through ambient drying orsupercritical drying as describe above may be further subjected toadditional drying under ambient pressure at 105 to 200° C. for about 0.5to 2 hours. Thereby, it becomes much easier to obtain an aerogelcomposite having low density and small pores. The additional drying maybe performed under ambient pressure at 150 to 200° C.

(Step of Crushing Block)

When the step of crushing a block is performed, the aerogel compositeblock obtained by drying is crushed to obtain an aerogel compositepowder. This can be achieved by placing the aerogel composite block in ajet mill, a roller mill, a bead mill, a hammer mill, or the like, andoperating the mill with a moderate rotational frequency for a moderateduration.

The aerogel composite powder obtained through the above steps can beapplied for a wide variety of uses with utilization of its thermalinsulation and flexibility. Examples of a method for improving thethermal insulation performance of an object include a method ofdispersing the powder in a liquid medium and spraying the dispersiononto an object; a method of spraying the powder onto an object having atacky surface; a method of mixing the powder with resin or the like andapplying the mixture onto an object; a method of filling voids possessedby an object with the powder; and a method of kneading the powder withresin or the like as a raw material of an object to obtain an extrudate.

EXAMPLES

Now, the present disclosure will be described in more detail withreference to the following Examples; however, these Examples are notintended to limit the present disclosure.

Example 1

[Aerogel Composite Powder]

Mixed together were 60.0 parts by mass of methyltrimethoxysilane, LS-530(produced by Shin-Etsu Chemical Co., Ltd., product name: hereinafter,abbreviated as “MTMS”), and 40.0 parts by mass ofdimethyldimethoxysilane, LS-520 (produced by Shin-Etsu Chemical Co.,Ltd., product name: hereinafter, abbreviated as “DMDMS”), as siliconcompounds, and 100.0 parts by mass of PL-2L (details on PL-2L are shownin Table 1, and the same is hereinafter applied for silicaparticle-containing raw materials), 40.0 parts by mass of water, and80.0 parts by mass of methanol, and thereto 0.10 parts by mass of aceticacid as an acid catalyst was added, and the resultant was reacted at 25°C. for 2 hours to afford a sol 1. To the sol 1 obtained, 40.0 parts bymass of aqueous ammonia with a concentration of 5% by mass as a basecatalyst was added, and the sol 1 was gelled at 60° C., and then aged at80° C. for 24 hours to afford a wet gel 1.

Thereafter, the wet gel 1 obtained was transferred into a plastic bottleand the plastic bottle was sealed, and thereafter the wet gel 1 wascrushed by using an Extreme Mill (produced by AS ONE Corporation,MX-1000XTS) at 27000 rpm for 10 minutes to afford a particulate wetgel 1. The particulate wet gel 1 obtained was soaked in 2500.0 parts bymass of methanol, and washed at 25° C. over 24 hours. This washingoperation was performed three times in total, where methanol wasreplaced with another one in each washing. Subsequently, the particulatewet gel washed was soaked in 2500.0 parts by mass of heptane as asolvent with low surface tension, and subjected to solvent displacementat 25° C. over 24 hours. This solvent displacement operation wasperformed three times in total, where heptane was replaced with anotherone in each solvent displacement. The particulate wet gel washed andsubjected to solvent displacement was dried under ambient pressure at40° C. for 96 hours, and thereafter further dried at 150° C. for 2hours. Finally, the particulate wet gel was sieved (produced by TOKYOSCREEN CO., LTD., mesh size: 45 μm, wire diameter: 32 μm) to afford anaerogel composite powder 1 having the structures represented by theabove formulas (4) and (5).

[Aerogel Composite Block]

The wet gel 1 obtained above was soaked in 2500.0 parts by mass ofmethanol, and washed at 60° C. over 12 hours. This washing operation wasperformed three times, where methanol was replaced with another one ineach washing. Subsequently, the wet gel washed was soaked in 2500.0parts by mass of heptane as a solvent with low surface tension, andsubjected to solvent displacement at 60° C. over 12 hours. This solventdisplacement operation was performed three times, where heptane wasreplaced with another one in each solvent displacement. The wet gelwashed and subjected to solvent displacement was dried under ambientpressure at 40° C. for 96 hours, and thereafter further dried at 150° C.for 2 hours to afford an aerogel composite block 1 having the structuresrepresented by the above formulas (4) and (5).

Example 2

Mixed together were 60.0 parts by mass of MTMS and 40.0 parts by mass ofbis(trimethoxysilyl)hexane, “KBM-3066” (produced by Shin-Etsu ChemicalCo., Ltd., product name), as silicon compounds, and 57.0 parts by massof ST-OZL-35 as a silica particle-containing raw material, 83.0 parts bymass of water, and 80.0 parts by mass of methanol, and thereto 0.10parts by mass of acetic acid as an acid catalyst and 20.0 parts by massof cetyltrimethylammonium bromide (produced by Wako Pure ChemicalIndustries, Ltd.: hereinafter, abbreviated as “CTAB”) as a cationicsurfactant were added, and the resultant was reacted at 25° C. for 2hours to afford a sol 2. To the sol 2 obtained, 40.0 parts by mass ofaqueous ammonia with a concentration of 5% as a base catalyst was added,and the sol 2 was gelled at 60° C., and then aged at 80° C. for 24 hoursto afford a wet gel 2. Thereafter, by using the wet gel 2 obtained, anaerogel composite powder 2 and an aerogel composite block 2 each havingthe structures represented by the above formulas (4) and (6) wereobtained in the same manner as in Example 1.

Example 3

Mixed together were 100.0 parts by mass of PL-2L as a silicaparticle-containing raw material, 100.0 parts by mass of water, 0.10parts by mass of acetic acid as an acid catalyst, and 120.0 parts bymass of urea as a thermally-hydrolyzable compound, and thereto 70.0parts by mass of MTMS and 30.0 parts by mass of DMDMS as siliconcompounds were added, and the resultant was reacted at 25° C. for 2hours to afford a sol 3. The sol 3 obtained was gelled at 60° C., andthen aged at 80° C. for 24 hours to afford a wet gel 3. Thereafter, byusing the wet gel 3 obtained, an aerogel composite powder 3 and anaerogel composite block 3 each having the structures represented by theabove formulas (4) and (5) were obtained in the same manner as inExample 1.

Example 4

Mixed together were 200.0 parts by mass of ST-OXS as a silicaparticle-containing raw material, 0.10 parts by mass of acetic acid asan acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant,and 120.0 parts by mass of urea as a thermally-hydrolyzable compound,and thereto 60.0 parts by mass of MTMS and 40.0 parts by mass of DMDMSas silicon compounds were added, and the resultant was reacted at 25° C.for 2 hours to afford a sol 4. The sol 4 obtained was gelled at 60° C.,and then aged at 80° C. for 24 hours to afford a wet gel 4. Thereafter,by using the wet gel 4 obtained, an aerogel composite powder 4 and anaerogel composite block 4 having the structures represented by the aboveformulas (4) and (5) were obtained in the same manner as in Example 1.

Example 5

Mixed together were 100.0 parts by mass of PL-2L-D as a silicaparticle-containing raw material, 100.0 parts by mass of water, 0.10parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass ofCTAB as a cationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMSand 40.0 parts by mass of DMDMS as silicon compounds, and the resultantwas reacted at 25° C. for 2 hours to afford a sol 5. The sol 5 obtainedwas gelled at 60° C., and then aged at 80° C. for 24 hours to afford awet gel 5. Thereafter, by using the wet gel 5 obtained, an aerogelcomposite powder 5 and an aerogel composite block 5 each having thestructures represented by the above formulas (4) and (5) were obtainedin the same manner as in Example 1.

Example 6

Mixed together were 87.0 parts by mass of PL-7 as a silicaparticle-containing raw material, 113.0 parts by mass of water, 0.10parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass ofCTAB as a cationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMSand 40.0 parts by mass of DMDMS as silicon compounds were added, and theresultant was reacted at 25° C. for 2 hours to afford a sol 6. The sol 6obtained was gelled at 60° C., and then aged at 80° C. for 24 hours toafford a wet gel 6. Thereafter, by using the wet gel 6 obtained, anaerogel composite powder 6 and an aerogel composite block 6 having thestructures represented by the above formulas (4) and (5) were obtainedin the same manner as in Example 1.

Example 7

Mixed together were 167.0 parts by mass of PL-1 as a silicaparticle-containing raw material, 33.0 parts by mass of water, 0.10parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass ofCTAB as a cationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMSand 40.0 parts by mass of DMDMS as silicon compounds were added, and theresultant was reacted at 25° C. for 2 hours to afford a sol 7. The sol 7obtained was gelled at 60° C., and then aged at 80° C. for 24 hours toafford a wet gel 7. Thereafter, by using the wet gel 7 obtained, anaerogel composite powder 7 and an aerogel composite block 7 each havingthe structures represented by the above formulas (4) and (5) wereobtained in the same manner as in Example 1.

Example 8

Mixed together were 100.0 parts by mass of ST-OYL as a silicaparticle-containing raw material, 100.0 parts by mass of water, 0.10parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass ofa block copolymer of polyoxyethylene and polyoxypropylene, F-127(produced by BASF SE, product name), as a nonionic surfactant, and 120.0parts by mass of urea as a thermally-hydrolyzable compound, and thereto80.0 parts by mass of MTMS as a silicon compound and 20.0 parts by massof X-22-160AS as a polysiloxane compound having the structurerepresented by the above formula (A) were added, and the resultant wasreacted at 25° C. for 2 hours to afford a sol 8. The sol 8 obtained wasgelled at 60° C., and then aged at 80° C. for 24 hours to afford a wetgel 8. Thereafter, by using the wet gel 8 obtained, an aerogel compositepowder 8 and an aerogel composite block 8 each having the structuresrepresented by the above formulas (1) and (4) were obtained in the samemanner as in Example 1.

Example 9

Mixed together were 200.0 parts by mass of PL-06L as a silicaparticle-containing raw material, 0.10 parts by mass of acetic acid asan acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant,and 120.0 parts by mass of urea as a thermally-hydrolyzable compound,and thereto 80.0 parts by mass of MTMS as a silicon compound and 20.0parts by mass of an alkoxy-modified polysiloxane compound withbifunctionality at each end having the structure represented by theabove formula (B) (hereinafter, referred to as “polysiloxane compoundA”) as a polysiloxane compound were added, and the resultant was reactedat 25° C. for 2 hours to afford a sol 9. The sol 9 obtained was gelledat 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 9.Thereafter, by using the wet gel 9 obtained, an aerogel composite powder9 and an aerogel composite block 9 each having the structuresrepresented by the above formulas (3) and (4) were obtained in the samemanner as in Example 1.

The above “polysiloxane compound A” had been synthesized as follows.First, 100.0 parts by mass of dimethylpolysiloxane with a silanol groupat both ends, XC96-723 (produced by Momentive Performance MaterialsInc., product name), 181.3 parts by mass of methyltrimethoxysilane, and0.50 parts by mass of t-butylamine were mixed together in a 1 Lthree-necked flask equipped with a stirrer, a thermometer, and a Dimrothcondenser, and reacted at 30° C. for 5 hours. Thereafter, the reactionsolution was heated under a reduced pressure of 1.3 kPa at 140° C. for 2hours for removal of volatile components to afford the alkoxy-modifiedpolysiloxane compound with bifunctionality at each end (polysiloxanecompound A).

Example 10

Mixed together were 100.0 parts by mass of PL-2L as a silicaparticle-containing raw material, 100.0 parts by mass of water, 0.10parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass ofCTAB as a cationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMSand 20.0 parts by mass of DMDMS as silicon compounds, and 20.0 parts bymass of the polysiloxane compound A as a polysiloxane compound wereadded, and the resultant was reacted at 25° C. for 2 hours to afford asol 10. The sol 10 obtained was gelled at 60° C., and then aged at 80°C. for 24 hours to afford a wet gel 10. Thereafter, by using the wet gel10 obtained, an aerogel composite powder 10 and an aerogel compositeblock 10 each having the structures represented by the above formulas(3), (4), and (5) were obtained in the same manner as in Example 1.

Example 11

Mixed together were 143.0 parts by mass of ST-OZL-35 as a silicaparticle-containing raw material, 57.0 parts by mass of water, 0.10parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass ofCTAB as a cationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMSand 20.0 parts by mass of DMDMS as silicon compounds, and 20.0 parts bymass of an alkoxy-modified polysiloxane compound with trifunctionalityat each end and having the structure represented by the above formula(B) (hereinafter, referred to as “polysiloxane compound B”) as apolysiloxane compound were added, and the resultant was reacted at 25°C. for 2 hours to afford a sol 11. The sol 11 obtained was gelled at 60°C., and then aged at 80° C. for 24 hours to afford a wet gel 11.Thereafter, by using the wet gel 11 obtained, an aerogel compositepowder 11 and an aerogel composite block 11 having the structuresrepresented by the above formulas (2), (4), and (5) were obtained in thesame manner as in Example 1.

The above “polysiloxane compound B” had been synthesized as follows.First, 100.0 parts by mass of XC96-723, 202.6 parts by mass oftetramethoxysilane, and 0.50 parts by mass of t-butylamine were mixedtogether in a 1 L three-necked flask equipped with a stirrer, athermometer, and a Dimroth condenser, and reacted at 30° C. for 5 hours.Thereafter, the reaction solution was heated under a reduced pressure of1.3 kPa at 140° C. for 2 hours for removal of volatile components toafford the alkoxy-modified polysiloxane compound with trifunctionalityat each end (polysiloxane compound B).

Example 12

Mixed together were 100.0 parts by mass of PL-2L and 50.0 parts by massof ST-OZL-35 as silica particle-containing raw materials, 50.0 parts bymass of water, 0.10 parts by mass of acetic acid as an acid catalyst,20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts bymass of urea as a thermally-hydrolyzable compound, and thereto 60.0parts by mass of MTMS and 20.0 parts by mass of DMDMS as siliconcompounds and 20.0 parts by mass of the polysiloxane compound A as apolysiloxane compound were added, and the resultant was reacted at 25°C. for 2 hours to afford a sol 12. The sol 12 obtained was gelled at 60°C., and then aged at 80° C. for 24 hours to afford a wet gel 12.Thereafter, by using the wet gel 12 obtained, an aerogel compositepowder 12 and an aerogel composite block 12 having the structuresrepresented by the above formulas (3), (4) and (5) were obtained in thesame manner as in Example 1.

Comparative Example 1

[Wet Gel, Aerogel]

Mixed together were 200.0 parts by mass of water, 0.10 parts by mass ofacetic acid as an acid catalyst, 20.0 parts by mass of CTAB as acationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 100.0 parts by mass of MTMSas a silicon compound was added, and the resultant was reacted at 25° C.for 2 hours to afford a sol 1C. The sol 1C obtained was gelled at 60°C., and then aged at 80° C. for 24 hours to afford a wet gel 1C.Thereafter, by using the wet gel 1C obtained, an aerogel powder 1C andan aerogel block 1C were obtained in the same manner as in Example 1.

Comparative Example 2

Mixed together were 200.0 parts by mass of water, 0.10 parts by mass ofacetic acid as an acid catalyst, 20.0 parts by mass of CTAB as acationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 80.0 parts by mass of MTMSand 20.0 parts by mass of DMDMS as silicon compounds were added, and theresultant was reacted at 25° C. for 2 hours to afford a sol 2C. The sol2C obtained was gelled at 60° C., and then aged at 80° C. for 24 hoursto afford a wet gel 2C. Thereafter, by using the wet gel 2C obtained, anaerogel powder 2C and an aerogel block 2C were obtained in the samemanner as in Example 1.

Comparative Example 3

Mixed together were 200.0 parts by mass of water, 0.10 parts by mass ofacetic acid as an acid catalyst, 20.0 parts by mass of CTAB as acationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 70.0 parts by mass of MTMSand 30.0 parts by mass of DMDMS as silicon compounds were added, and theresultant was reacted at 25° C. for 2 hours to afford a sol 3C. The sol3C obtained was gelled at 60° C., and then aged at 80° C. for 24 hoursto afford a wet gel 3C. Thereafter, by using the wet gel 3C obtained, anaerogel powder 3C and an aerogel block 3C were obtained in the samemanner as in Example 1.

Comparative Example 4

Mixed together were 200.0 parts by mass of water, 0.10 parts by mass ofacetic acid as an acid catalyst, 20.0 parts by mass of CTAB as acationic surfactant, and 120.0 parts by mass of urea as athermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMSand 40.0 parts by mass of DMDMS as silicon compounds were added, and theresultant was reacted at 25° C. for 2 hours to afford a sol 4C. The sol4C obtained was gelled at 60° C., and then aged at 80° C. for 24 hoursto afford a wet gel 4C. Thereafter, by using the wet gel 4C obtained, anaerogel powder 4C and an aerogel block 4C were obtained in the samemanner as in Example 1.

The modes of the silica particle-containing raw material in Examples aresummarized in Table 1. The types and amounts of the Si raw materials(silicon compound and polysiloxane compound) added, and the amounts ofthe silica particle-containing raw material added are summarized inTable 2.

TABLE 1 Silica particle-containing raw material Silica particle AverageSolid primary content particle [% by Item Name Supplier Type Shapediameter [nm] weight] Example 1 PL-2L FUSO CHEMICAL colloidal sphere 2020 CO., LTD. silica Example 2 ST-OZL-35 Nissan Chemical colloidal sphere100 35 Industries, Ltd. silica Example 3 PL-2L FUSO CHEMICAL colloidalsphere 20 20 CO., LTD. silica Example 4 ST-OXS Nissan Chemical colloidalsphere 5 10 Industries, Ltd. silica Example 5 PL-2L-D FUSO colloidalsphere 20 20 CHEMICAL silica CO., LTD. Example 6 PL-7 FUSO CHEMICALcolloidal cocoon 75 23 CO., LTD. silica Example 7 PL-1 FUSO CHEMICALcolloidal association 15 12 CO., LTD. silica Example 8 ST-OYL NissanChemical colloidal sphere 70 20 Industries, Ltd. silica Example 9 PL-06LFUSO CHEMICAL colloidal sphere 7 6 CO., LTD. silica Example 10 PL-2LFUSO CHEMICAL colloidal sphere 20 20 CO., LTD. silica Example 11ST-OZL-35 Nissan Chemical colloidal sphere 100 35 Industries, Ltd.silica Example 12 PL-2L FUSO CHEMICAL colloidal sphere 20 20 CO., LTD.silica ST-OZL-35 Nissan Chemical colloidal sphere 100 35 Industries,Ltd. silica

TABLE 2 Silica particle-containing Si raw material raw material Amountadded Amount added [part by [part by Item Type mass] mass] Example 1MTMS 60.0 100 DMDMS 40.0 Example 2 MTMS 60.0 57 bis(trimethoxy- 40.0silyl)hexane Example 3 MTMS 70.0 100 DMDMS 30.0 Example 4 MTMS 60.0 200DMDMS 40.0 Example 5 MTMS 60.0 100 DMDMS 40.0 Example 6 MTMS 60.0 87DMDMS 40.0 Example 7 MTMS 60.0 167 DMDMS 40.0 Example 8 MTMS 80.0 100X-22-160AS 20.0 Example 9 MTMS 80.0 200 polysiloxane 20.0 compound AExample 10 MTMS 60.0 100 DMDMS 20.0 polysiloxane 20.0 compound A Example11 MTMS 60.0 143 DMDMS 20.0 polysiloxane 20.0 compound B Example 12 MTMS60.0 100 (PL-2L) DMDMS 20.0 50 (ST-OZL-35) poly siloxane 20.0 compound AComparative MTMS 100.0 — Example 1 Comparative MTMS 80.0 — Example 2DMDMS 20.0 Comparative MTMS 70.0 — Example 3 DMDMS 30.0 Comparative MTMS60.0 — Example 4 DMDMS 40.0

[Evaluations]

Measurement or evaluation was conducted for the wet gels, aerogelcomposite powders, and aerogel composite blocks obtained in Examples,and the wet gels, aerogel powders, and aerogel blocks obtained inComparative Examples, under the following conditions. Evaluation resultsfor the gelling time in the step of forming a wet gel, the state of anaerogel composite block or aerogel block in ambient pressure drying ofmethanol-displaced gel, and the thermal conductivity, compressionmodulus, density, porosity, and average particle diameter D50 of anaerogel composite powder or aerogel powder are summarized in Table 3.

(1) Measurement of Gelling Time

Into a 100 mL airtight PP container, 30 mL of the sol obtained in eachof Examples and Comparative Examples was transferred, which was used asa measurement sample. Subsequently, the measurement sample was placed inthe thermostatic dryer “DVS402” (produced by Yamato Scientific Co.,Ltd., product name) set at 60° C., and the time from the entrance togelling was measured.

(2) State of Aerogel Composite Block or Aerogel Block in AmbientPressure Drying of Methanol-Displaced Gel

In 150.0 parts by mass of methanol, 30.0 parts by mass of the wet gelobtained in each of Examples and Comparative Examples was soaked, andwashed at 60° C. over 12 hours. This washing operation was performedthree times, where methanol was replaced with another one in eachwashing. Subsequently, the wet gel washed was processed into a piece ina size of 100×100×100 mm³ by using a blade with a blade angle ofapproximately 20 to 25 degrees, and the piece was used as a measurementsample before drying. By using the thermostat with a safety vent “SPH(H)-202” (produced by ESPEC CORP., product name), the measurement samplebefore drying obtained was dried at 60° C. for 2 hours and at 100° C.for 3 hours, and then further dried at 150° C. for 2 hours to afford ameasurement sample after drying (the solvent evaporation rate and so onwere not controlled in any way). Then, the volume shrinkage of thesample before and after drying, SV, was determined by using thefollowing equation. A case that the volume shrinkage, SV, was 5% orlower was rated as “not shrunk”, and a case that the volume shrinkage,SV, was 5% or higher was rated as “shrunk”.SV=(V ₀ −V ₁)/V ₀×100

In the equation, V₀ denotes the volume of a sample before drying; and V₁denotes the volume of the sample after drying.

(3) Measurement of Average Particle Diameter, D50

An aerogel composite powder or aerogel powder was added to ethanol to aconcentration of 0.5% by mass, and the resultant was vibrated with a 50W ultrasonic homogenizer for 20 minutes. Thereafter, 10 mL of thedispersion was injected into a Microtrac MT3000 (produced by NikkisoCo., Ltd., product name), and the particle diameter was measured at 25°C. with a refractive index of 1.3 and absorption of 0. And then, aparticle diameter at 50% of the cumulative value (volume-based) in theparticle size distribution was used as the average particle diameter,D50.

(4) Measurement of Thermal Conductivity

An aerogel composite block or aerogel block was processed into a piecein a size of 150×150×100 mm³ by using a blade with a blade angle ofapproximately 20 to 25 degrees, and the piece was used as a measurementsample. Subsequently, the measurement sample was shaped with a sandpaper of #1500 or finer to thoroughly smooth the surface, as necessary.Before measurement of thermal conductivity, the measurement sampleobtained was dried by using the thermostatic dryer “DVS402” (produced byYamato Scientific Co., Ltd., product name) under the atmosphericpressure at 100° C. for 30 minutes. The measurement sample was thentransferred into a desiccator and cooled to 25° C. Thus, a measurementsample for measurement of the thermal conductivity was obtained.

Measurement of thermal conductivity was conducted by using the thermalconductivity analyzer based on a steady state method “HFM 436 Lambda”(produced by NETZSCH, product name). Measurement conditions were setsuch that measurement was performed under the atmospheric pressure at anaverage temperature of 25° C. The measurement sample obtained asdescribed above was sandwiched between an upper heater and a lowerheater with a load of 0.3 MPa, the temperature difference, ΔT, was setto 20° C., and the upper surface temperature, lower surface temperature,and so on of the measurement sample were measured while the heat flowwas adjusted to a one-dimensional heat flow by using a guard heater. Thethermal resistance, R_(S), of the measurement sample was determined byusing the following equation:R _(S) =N((T _(U) −T _(L))/Q)−R _(O)wherein T_(U) denotes the upper surface temperature of the measurementsample; T_(L) denotes the lower surface temperature of the measurementsample; R_(O) denotes the contact thermal resistance of the upper/lowerinterface; and Q denotes output from a heat flux meter. N denotes aproportionality coefficient, and had been determined in advance by usinga calibration sample.

From the thermal resistance, R_(S), obtained, the thermal conductivity,λ, of the measurement sample was determined by using the followingequation:λ=d/R _(S)wherein d denotes the thickness of the measurement sample.

(5) Measurement of Compression Modulus

An aerogel composite block or aerogel block was processed into a cube(dice) of 7.0×7.0×7.0 mm by using a blade with a blade angle ofapproximately 20 to 25 degrees, and the cube was used as a measurementsample. Subsequently, the measurement sample was shaped with a sandpaper of #1500 or finer to thoroughly smooth the surface, as necessary.Before measurement, the measurement sample obtained was dried by usingthe thermostatic dryer “DVS402” (produced by Yamato Scientific Co.,Ltd., product name) under the atmospheric pressure at 100° C. for 30minutes. The measurement sample was then transferred into a desiccatorand cooled to 25° C. Thus, a measurement sample for measurement of thecompression modulus was obtained.

For the measurement apparatus, the compact table-top tester “EZ Test”(produced by Shimadzu Corporation, product name) was used. A load cellof 500 N was used. An upper platen (ϕ20 mm) and lower platen (ϕ118 mm)each made of stainless steel were used as jigs for compressionmeasurement. The measurement sample was set between the upper platen andlower platen positioned in parallel, and compressed at a speed of 1mm/min. The measurement temperature was 25° C., and the measurement wasterminated at a point of time when a load of higher than 500 N wasapplied or when the measurement sample was broken. Here, the strain, ε,was determined by using the following equation:ε=Δd/d1wherein Δd denotes the change in thickness (mm) of the measurementsample caused by a load; and d1 denotes the thickness (mm) of themeasurement sample before application of a load.

The compressive stress (MPa), σ, was determined by using the followingequation:σ=F/Awherein F denotes compressive force (N); and A denotes thecross-sectional area (mm²) of the measurement sample before applicationof a load.

The compression modulus (MPa), E, was determined in a range ofcompressive force from 0.1 to 0.2 N by using the following equation:E=(σ₂−σ₁)/(ε₂−ε₁)wherein σ₁ denotes compressive stress (MPa) measured at a compressiveforce of 0.1 N; σ₂ denotes compressive stress (MPa) measured at acompressive force of 0.2 N; ε₁ denotes compressive strain measured at acompressive stress of σ₁; and ε₂ denotes compressive strain measured ata compressive stress of σ₂.

(6) Measurement of Density and Porosity

The density and porosity of an aerogel composite block or aerogel block,with regard to the pore (through-hole) connected as a three-dimensionalnetwork, were measured by using mercury porosimetry in accordance withDIN 66133. The measurement temperature was room temperature (25° C.),and an AutoPore IV9520 (produced by Shimadzu Corporation, product name)was used for the measurement apparatus.

TABLE 3 Wet gel Aerogel composite (aerogel) State of gel after BlockGelling ambient pressure Powder Thermal Compressive time drying ofmethanol- D50 conductivity modulus Density Porosity Item [min] displacedgel [μm] [W/(m · K)] [MPa] [g/cm³] [%] Example 1 30 not shrunk 24 0.0300.44 0.19 85.3 Example 2 60 not shrunk 32 0.022 0.98 0.18 89.2 Example 330 not shrunk 18 0.027 1.37 0.19 86.1 Example 4 60 not shrunk 25 0.0300.43 0.19 86.7 Example 5 60 not shrunk 23 0.030 0.51 0.19 86.5 Example 630 not shrunk 26 0.028 0.55 0.19 86.2 Example 7 30 not shrunk 23 0.0300.42 0.19 86.4 Example 8 60 not shrunk 21 0.018 1.47 0.18 90.6 Example 960 not shrunk 19 0.018 1.68 0.18 91.2 Example 10 30 not shrunk 20 0.0230.94 0.18 89.3 Example 11 60 not shrunk 27 0.018 1.39 0.19 90.1 Example12 30 not shrunk 25 0.022 1.08 0.19 89.6 Comparative 180 shrunk 12 0.0177.40 0.17 91.2 Example 1 (with crack) Comparative 180 shrunk 15 0.0284.35 0.18 90.8 Example 2 (with crack) Comparative 210 shrunk 20 0.0411.25 0.18 86.8 Example 3 (with crack) Comparative 240 not shrunk 360.045 0.15 0.19 86.4 Example 4

Table 3 shows that each of the aerogel composite powders and blocks inExamples had a short gelling time in the step of forming a wet gel andwas excellent in reactivity, and had good shrinkage resistance inambient pressure drying of methanol-displaced gel. In addition, it isunderstood that each of the aerogel composite blocks in Examples has alow thermal conductivity and low compression modulus, and thecorresponding aerogel composite powder with the same composition is alsosuperior in both thermal insulation and flexibility.

In each of Comparative Examples 1 to 3, in contrast, the gelling time inthe step of forming a wet gel was long, and the gel shrunk and a crackwas generated in the surface in ambient pressure drying ofmethanol-displaced gel. In addition, one of thermal conductivity andflexibility was poor. In Comparative Example 4, the shrinkage resistanceand flexibility were sufficient, but the gelling time was long and thethermal conductivity was high.

REFERENCE SIGNS LIST

-   -   1 . . . aerogel particle    -   2 . . . silica particle    -   3 . . . pore    -   10 . . . aerogel composite    -   L . . . circumscribed rectangle

The invention claimed is:
 1. An aerogel composite powder comprising: anaerogel component; and a silica particle, wherein the aerogel compositepowder comprises a ladder-type structure including struts and a bridge,wherein the bridge has a structure represented by the following formula(2):

wherein R⁵ and R⁶ each independently represent an alkyl group or an arylgroup; and b represents an integer of 1 to
 50. 2. The aerogel compositepowder according to claim 1, having: a three-dimensional networkskeleton formed of the aerogel component and the silica particle; and apore.
 3. An aerogel composite powder comprising a silica particle as acomponent constituting a three-dimensional network skeleton, wherein theaerogel composite powder comprises a ladder-type structure includingstruts and a bridge, wherein the bridge has a structure represented bythe following formula (2):

wherein R⁵ and R⁶ each independently represent an alkyl group or an arylgroup; and b represents an integer of 1 to
 50. 4. An aerogel compositepowder as a dried product of a wet gel, wherein the wet gel is acondensate of a sol comprising: a silica particle; and at least oneselected from the group consisting of a silicon compound having ahydrolyzable functional group or a condensable functional group and ahydrolysis product of the silicon compound having a hydrolyzablefunctional group, wherein the silicon compound further comprises apolysiloxane compound having a hydrolysable functional group or acondensable functional group, and wherein the polysiloxane compoundincludes a compound having a structure represented by the followingformula (B):

wherein R^(1b) represents an alkyl group, an alkoxy group, or an arylgroup; R^(2b) and R^(3b) each independently represent an alkoxy group;R^(4b) and R^(5b) each independently represent an alkyl group or an arylgroup; and m represents an integer of 1 to
 50. 5. The aerogel compositepowder according to claim 1, as a dried product of a wet gel, whereinthe wet gel is a condensate of a sol comprising: a silica particle; andat least one selected from the group consisting of a silicon compoundhaving a hydrolyzable functional group or a condensable functional groupand a hydrolysis product of the silicon compound having a hydrolyzablefunctional group.
 6. The aerogel composite powder according to claim 1,having a ladder-type structure represented by the following formula (3):

wherein R⁵, R⁶, R⁷, and R⁸ each independently represent an alkyl groupor an aryl group; a and c each independently represent an integer of 1to 3000; and b represents an integer of 1 to
 50. 7. The aerogelcomposite powder according to claim 1, wherein an average primaryparticle diameter of the silica particle is 1 to 500 nm.
 8. The aerogelcomposite powder according to claim 1, wherein a shape of the silicaparticle is spherical.
 9. The aerogel composite powder according to anyclaim 1, wherein the silica particle is an amorphous silica particle.10. The aerogel composite powder according to claim 9, wherein theamorphous silica particle is at least one selected from the groupconsisting of a fused silica particle, a fumed silica particle, and acolloidal silica particle.
 11. The aerogel composite powder according toclaim 1, wherein an average particle diameter D50 is 1 to 1000 μm. 12.The aerogel composite powder according to claim 3, as a dried product ofa wet gel, wherein the wet gel is a condensate of a sol comprising: asilica particle; and at least one selected from the group consisting ofa silicon compound having a hydrolyzable functional group or acondensable functional group and a hydrolysis product of the siliconcompound having a hydrolyzable functional group.
 13. The aerogelcomposite powder according to claim 3, having a ladder-type structurerepresented by the following formula (3):

wherein R⁵, R⁶, R⁷, and R⁸ each independently represent an alkyl groupor an aryl group; a and c each independently represent an integer of 1to 3000; and b represents an integer of 1 to
 50. 14. The aerogelcomposite powder according to claim 3, wherein an average primaryparticle diameter of the silica particle is 1 to 500 nm.
 15. The aerogelcomposite powder according to claim 3, wherein a shape of the silicaparticle is spherical.
 16. The aerogel composite powder according to anyclaim 3, wherein the silica particle is an amorphous silica particle.17. The aerogel composite powder according to claim 16, wherein theamorphous silica particle is at least one selected from the groupconsisting of a fused silica particle, a fumed silica particle, and acolloidal silica particle.
 18. The aerogel composite powder according toclaim 3, wherein an average particle diameter D50 is 1 to 1000 μm. 19.The aerogel composite powder according to claim 4, wherein an averageprimary particle diameter of the silica particle is 1 to 500 nm.
 20. Theaerogel composite powder according to claim 4, wherein a shape of thesilica particle is spherical.